Colon and Rectal

A growing body of evidence has shown that people who regularly take aspirin have a lower risk for colorectal cancer (CRC) and are less likely to die if they do develop the disease.

A 2020 meta-analysis, for instance, found that 325 mg of daily aspirin — the typical dose in a single tablet — conferred a 35% reduced risk of developing CRC, and a highly cited The Lancet study from 2010 found that a low dose of daily aspirin reduced the incidence of colon cancer by 24% and colon cancer deaths by 35% over 20 years.

The evidence surrounding aspirin and CRC is so intriguing that more than 70,000 people are currently participating in more than two dozen clinical studies worldwide, putting aspirin through its paces as an intervention in CRC.

But what, exactly, is aspirin doing?

We know that aspirin inhibits cyclooxygenase (COX) enzymes — COX-1 and COX-2, specifically — and that the COX-2 pathway is implicated in the development and progression of CRC, explained Marco Scarpa, MD, PhD, staff surgeon at the University of Padova in Padova, Italy.

“However, the new thing we’ve found is that aspirin may have a direct role in enhancing immunosurveillance,” Dr. Scarpa said in an interview.

In April, Dr. Scarpa’s team published a paper in Cancer describing a mechanism that provides deeper insight into the aspirin-CRC connection.

Dr. Scarpa heads up the IMMUNOREACT study group, a collaboration of dozens of researchers across Italy running studies on immunosurveillance in rectal cancer. In the baseline study, IMMUNOREACT 1, the team created and analyzed a database of records from 238 patients who underwent surgery for CRC at the Azienda Ospedale Università di Padova, Padova, Italy, from 2015 to 2019.

Using the same database, the latest findings from IMMUNOREACT 7 focused on the fate of the 31 patients (13%) who used aspirin regularly.

The researchers found that regular aspirin use did not appear to affect colorectal tumor stage at diagnosis, but tumor grading was significantly lower overall, especially in patients with BRAF mutations. Regular aspirin users were also less likely to have nodal metastases and metastatic lymph nodes, and this effect was more pronounced in patients with proximal (right-sided) colon cancer vs distal (left-sided).

Most notably, IMMUNOREACT 7 revealed that aspirin has beneficial effects on the CRC immune microenvironment.

The team found that aspirin directly boosts the presence of antigens on gastrointestinal epithelial tumor cells, which can direct the body’s immune response to combat the cancer.

At a macro level, the aspirin users in the study were more likely to have high levels of tumor-infiltrating lymphocytes (TILs). Dr. Scarpa’s team had previously shown that high levels of CD8+ and CD3+ TILs were predictive of successful neoadjuvant therapy in rectal cancer.

Cytotoxic CD8+ T cells are central to the anticancer immune response, and in the latest study, a high ratio of CD8+/CD3+ T cells was more common in aspirin users, suggesting a stronger presence of cancer-killing CD8+ cells. Expression of CD8 beta+, an activation marker of CD8+ cells, was also enhanced in aspirin users.

The most significant discovery, according to Dr. Scarpa, was that aspirin users were more likely to show high expression of CD80 on the surface of their rectal epithelial cells.

CD80 is a molecule that allows T cells to identify the tumor cell as foreign and kill it. Although cancer cells can downregulate their CD80 to avoid detection by T cells, the study suggests that aspirin appears to help foil this strategy by boosting the production of CD80 on the surface of the tumor cells.

The researchers confirmed the clinical findings by showing that aspirin increased CD80 gene expression in lab-cultivated CRC cells.

“We didn’t expect the activation through CD80,” said Dr. Scarpa. “This means that aspirin can act on this very first interaction between the epithelial cell and the CD8+ lymphocyte.”

Overall, these new data suggest that aspirin helps activate the immune system, which helps explain its potential chemopreventive effect in CRC.

However, one puzzling result was that aspirin boosted expression of PD-L1 genes in the CRC cells, said Joanna Davies, DPhil, an immunologist who heads up the San Diego Biomedical Research Institute, San Diego, California, and was not involved in the study.

PD-L1 serves as an “off” switch for patrolling T cells, which protects the tumor cell from being recognized.

“If aspirin is inducing PD-L1 on cancer cells, that is a potential problem,” said Dr. Davies. “An ideal therapy might be the combination of aspirin to enhance the CD8 T cells in the tumor and immune checkpoint blockade to block PD-L1.”

David Kerr, CBE, MD, DSc, agreed that high-dose aspirin plus immunotherapy might be “a wee bit more effective.” However, the combination would be blocked by the economics of drug development: “Will anybody ever do a trial of 10,000 patients to prove that? Not on your nelly,” said Dr. Kerr, professor of cancer medicine at the University of Oxford, Oxford, England.

Despite the small patient numbers in the study, Dr. Kerr felt encouraged by the IMMUNOREACT analysis. “It’s a plausible piece of science and some quite promising work on the tumor immune microenvironment and the effects of aspirin on it,” Dr. Kerr said in a recent commentary for this news organization.

Dr. Scarpa and Dr. Davies had no conflicts of interest to declare.

A version of this article appeared on Medscape.com .

A growing body of evidence has shown that people who regularly take aspirin have a lower risk for colorectal cancer (CRC) and are less likely to die if they do develop the disease.

A 2020 meta-analysis, for instance, found that 325 mg of daily aspirin — the typical dose in a single tablet — conferred a 35% reduced risk of developing CRC, and a highly cited The Lancet study from 2010 found that a low dose of daily aspirin reduced the incidence of colon cancer by 24% and colon cancer deaths by 35% over 20 years.

The evidence surrounding aspirin and CRC is so intriguing that more than 70,000 people are currently participating in more than two dozen clinical studies worldwide, putting aspirin through its paces as an intervention in CRC.

But what, exactly, is aspirin doing?

We know that aspirin inhibits cyclooxygenase (COX) enzymes — COX-1 and COX-2, specifically — and that the COX-2 pathway is implicated in the development and progression of CRC, explained Marco Scarpa, MD, PhD, staff surgeon at the University of Padova in Padova, Italy.

“However, the new thing we’ve found is that aspirin may have a direct role in enhancing immunosurveillance,” Dr. Scarpa said in an interview.

In April, Dr. Scarpa’s team published a paper in Cancer describing a mechanism that provides deeper insight into the aspirin-CRC connection.

Dr. Scarpa heads up the IMMUNOREACT study group, a collaboration of dozens of researchers across Italy running studies on immunosurveillance in rectal cancer. In the baseline study, IMMUNOREACT 1, the team created and analyzed a database of records from 238 patients who underwent surgery for CRC at the Azienda Ospedale Università di Padova, Padova, Italy, from 2015 to 2019.

Using the same database, the latest findings from IMMUNOREACT 7 focused on the fate of the 31 patients (13%) who used aspirin regularly.

The researchers found that regular aspirin use did not appear to affect colorectal tumor stage at diagnosis, but tumor grading was significantly lower overall, especially in patients with BRAF mutations. Regular aspirin users were also less likely to have nodal metastases and metastatic lymph nodes, and this effect was more pronounced in patients with proximal (right-sided) colon cancer vs distal (left-sided).

Most notably, IMMUNOREACT 7 revealed that aspirin has beneficial effects on the CRC immune microenvironment.

The team found that aspirin directly boosts the presence of antigens on gastrointestinal epithelial tumor cells, which can direct the body’s immune response to combat the cancer.

At a macro level, the aspirin users in the study were more likely to have high levels of tumor-infiltrating lymphocytes (TILs). Dr. Scarpa’s team had previously shown that high levels of CD8+ and CD3+ TILs were predictive of successful neoadjuvant therapy in rectal cancer.

Cytotoxic CD8+ T cells are central to the anticancer immune response, and in the latest study, a high ratio of CD8+/CD3+ T cells was more common in aspirin users, suggesting a stronger presence of cancer-killing CD8+ cells. Expression of CD8 beta+, an activation marker of CD8+ cells, was also enhanced in aspirin users.

The most significant discovery, according to Dr. Scarpa, was that aspirin users were more likely to show high expression of CD80 on the surface of their rectal epithelial cells.

CD80 is a molecule that allows T cells to identify the tumor cell as foreign and kill it. Although cancer cells can downregulate their CD80 to avoid detection by T cells, the study suggests that aspirin appears to help foil this strategy by boosting the production of CD80 on the surface of the tumor cells.

The researchers confirmed the clinical findings by showing that aspirin increased CD80 gene expression in lab-cultivated CRC cells.

“We didn’t expect the activation through CD80,” said Dr. Scarpa. “This means that aspirin can act on this very first interaction between the epithelial cell and the CD8+ lymphocyte.”

Overall, these new data suggest that aspirin helps activate the immune system, which helps explain its potential chemopreventive effect in CRC.

However, one puzzling result was that aspirin boosted expression of PD-L1 genes in the CRC cells, said Joanna Davies, DPhil, an immunologist who heads up the San Diego Biomedical Research Institute, San Diego, California, and was not involved in the study.

PD-L1 serves as an “off” switch for patrolling T cells, which protects the tumor cell from being recognized.

“If aspirin is inducing PD-L1 on cancer cells, that is a potential problem,” said Dr. Davies. “An ideal therapy might be the combination of aspirin to enhance the CD8 T cells in the tumor and immune checkpoint blockade to block PD-L1.”

David Kerr, CBE, MD, DSc, agreed that high-dose aspirin plus immunotherapy might be “a wee bit more effective.” However, the combination would be blocked by the economics of drug development: “Will anybody ever do a trial of 10,000 patients to prove that? Not on your nelly,” said Dr. Kerr, professor of cancer medicine at the University of Oxford, Oxford, England.

Despite the small patient numbers in the study, Dr. Kerr felt encouraged by the IMMUNOREACT analysis. “It’s a plausible piece of science and some quite promising work on the tumor immune microenvironment and the effects of aspirin on it,” Dr. Kerr said in a recent commentary for this news organization.

Dr. Scarpa and Dr. Davies had no conflicts of interest to declare.

A version of this article appeared on Medscape.com .

A growing body of evidence has shown that people who regularly take aspirin have a lower risk for colorectal cancer (CRC) and are less likely to die if they do develop the disease.

A 2020 meta-analysis, for instance, found that 325 mg of daily aspirin — the typical dose in a single tablet — conferred a 35% reduced risk of developing CRC, and a highly cited The Lancet study from 2010 found that a low dose of daily aspirin reduced the incidence of colon cancer by 24% and colon cancer deaths by 35% over 20 years.

The evidence surrounding aspirin and CRC is so intriguing that more than 70,000 people are currently participating in more than two dozen clinical studies worldwide, putting aspirin through its paces as an intervention in CRC.

But what, exactly, is aspirin doing?

We know that aspirin inhibits cyclooxygenase (COX) enzymes — COX-1 and COX-2, specifically — and that the COX-2 pathway is implicated in the development and progression of CRC, explained Marco Scarpa, MD, PhD, staff surgeon at the University of Padova in Padova, Italy.

“However, the new thing we’ve found is that aspirin may have a direct role in enhancing immunosurveillance,” Dr. Scarpa said in an interview.

In April, Dr. Scarpa’s team published a paper in Cancer describing a mechanism that provides deeper insight into the aspirin-CRC connection.

Dr. Scarpa heads up the IMMUNOREACT study group, a collaboration of dozens of researchers across Italy running studies on immunosurveillance in rectal cancer. In the baseline study, IMMUNOREACT 1, the team created and analyzed a database of records from 238 patients who underwent surgery for CRC at the Azienda Ospedale Università di Padova, Padova, Italy, from 2015 to 2019.

Using the same database, the latest findings from IMMUNOREACT 7 focused on the fate of the 31 patients (13%) who used aspirin regularly.

The researchers found that regular aspirin use did not appear to affect colorectal tumor stage at diagnosis, but tumor grading was significantly lower overall, especially in patients with BRAF mutations. Regular aspirin users were also less likely to have nodal metastases and metastatic lymph nodes, and this effect was more pronounced in patients with proximal (right-sided) colon cancer vs distal (left-sided).

Most notably, IMMUNOREACT 7 revealed that aspirin has beneficial effects on the CRC immune microenvironment.

The team found that aspirin directly boosts the presence of antigens on gastrointestinal epithelial tumor cells, which can direct the body’s immune response to combat the cancer.

At a macro level, the aspirin users in the study were more likely to have high levels of tumor-infiltrating lymphocytes (TILs). Dr. Scarpa’s team had previously shown that high levels of CD8+ and CD3+ TILs were predictive of successful neoadjuvant therapy in rectal cancer.

Cytotoxic CD8+ T cells are central to the anticancer immune response, and in the latest study, a high ratio of CD8+/CD3+ T cells was more common in aspirin users, suggesting a stronger presence of cancer-killing CD8+ cells. Expression of CD8 beta+, an activation marker of CD8+ cells, was also enhanced in aspirin users.

The most significant discovery, according to Dr. Scarpa, was that aspirin users were more likely to show high expression of CD80 on the surface of their rectal epithelial cells.

CD80 is a molecule that allows T cells to identify the tumor cell as foreign and kill it. Although cancer cells can downregulate their CD80 to avoid detection by T cells, the study suggests that aspirin appears to help foil this strategy by boosting the production of CD80 on the surface of the tumor cells.

The researchers confirmed the clinical findings by showing that aspirin increased CD80 gene expression in lab-cultivated CRC cells.

“We didn’t expect the activation through CD80,” said Dr. Scarpa. “This means that aspirin can act on this very first interaction between the epithelial cell and the CD8+ lymphocyte.”

Overall, these new data suggest that aspirin helps activate the immune system, which helps explain its potential chemopreventive effect in CRC.

However, one puzzling result was that aspirin boosted expression of PD-L1 genes in the CRC cells, said Joanna Davies, DPhil, an immunologist who heads up the San Diego Biomedical Research Institute, San Diego, California, and was not involved in the study.

PD-L1 serves as an “off” switch for patrolling T cells, which protects the tumor cell from being recognized.

“If aspirin is inducing PD-L1 on cancer cells, that is a potential problem,” said Dr. Davies. “An ideal therapy might be the combination of aspirin to enhance the CD8 T cells in the tumor and immune checkpoint blockade to block PD-L1.”

David Kerr, CBE, MD, DSc, agreed that high-dose aspirin plus immunotherapy might be “a wee bit more effective.” However, the combination would be blocked by the economics of drug development: “Will anybody ever do a trial of 10,000 patients to prove that? Not on your nelly,” said Dr. Kerr, professor of cancer medicine at the University of Oxford, Oxford, England.

Despite the small patient numbers in the study, Dr. Kerr felt encouraged by the IMMUNOREACT analysis. “It’s a plausible piece of science and some quite promising work on the tumor immune microenvironment and the effects of aspirin on it,” Dr. Kerr said in a recent commentary for this news organization.

Dr. Scarpa and Dr. Davies had no conflicts of interest to declare.

A version of this article appeared on Medscape.com .

When doctors and patients consider the appendix, it’s often with urgency. In cases of appendicitis, the clock could be ticking down to a life-threatening burst. Thus, despite recent research suggesting antibiotics could be an alternative therapy, appendectomy remains standard for uncomplicated appendicitis.

But what if removing the appendix could raise the risk for gastrointestinal (GI) diseases like irritable bowel syndrome and colorectal cancer? That’s what some emerging science suggests. And though the research is early and mixed, it’s enough to give some health professionals pause.

“If there’s no reason to remove the appendix, then it’s better to have one,” said Heather Smith, PhD, a comparative anatomist at Midwestern University, Glendale, Arizona. Preemptive removal is not supported by the evidence, she said.

To be fair, we’ve come a long way since 1928, when American physician Miles Breuer, MD, suggested that people with infected appendixes should be left to perish, so as to remove their inferior DNA from the gene pool (he called such people “uncivilized” and “candidates for extinction”). Charles Darwin, while less radical, believed the appendix was at best useless — a mere vestige of our ancestors switching diets from leaves to fruits.

What we know now is that the appendix isn’t just a troublesome piece of worthless flesh. Instead, it may act as a safe house for friendly gut bacteria and a training camp for the immune system. It also appears to play a role in several medical conditions, from ulcerative colitis and colorectal cancer to Parkinson’s disease and lupus. The roughly 300,000 Americans who undergo appendectomy each year should be made aware of this, some experts say. But the frustrating truth is, scientists are still trying to figure out in which cases having an appendix is protective and in which we may be better off without it.
 

A ‘Worm’ as Intestinal Protection

The appendix is a blind pouch (meaning its ending is closed off) that extends from the large intestine. Not all mammals have one; it’s been found in several species of primates and rodents, as well as in rabbits, wombats, and Florida manatees, among others (dogs and cats don’t have it). While a human appendix “looks like a little worm,” Dr. Smith said, these anatomical structures come in various sizes and shapes. Some are thick, as in a beaver, while others are long and spiraling, like a rabbit’s.

Comparative anatomy studies reveal that the appendix has evolved independently at least 29 times throughout mammalian evolution. This suggests that “it has some kind of an adaptive function,” Dr. Smith said. When French scientists analyzed data from 258 species of mammals, they discovered that those that possess an appendix live longer than those without one. A possible explanation, the researchers wrote, may lie with the appendix’s role in preventing diarrhea.

Their 2023 study supported this hypothesis. Based on veterinary records of 45 different species of primates housed in a French zoo, the scientists established that primates with appendixes are far less likely to suffer severe diarrhea than those that don’t possess this organ. The appendix, it appears, might be our tiny weapon against bowel troubles.

For immunologist William Parker, PhD, a visiting scholar at the University of North Carolina at Chapel Hill, these data are “about as good as we could hope for” in support of the idea that the appendix might protect mammals from GI problems. An experiment on humans would be unethical, Dr. Parker said. But observational studies offer clues.

One study showed that compared with people with an intact appendix, young adults with a history of appendectomy have more than double the risk of developing a serious infection with non-typhoidal Salmonella of the kind that would require hospitalization.
 

A ‘Safe House’ for Bacteria

Such studies add weight to a theory that Dr. Parker and his colleagues developed back in 2007: That the appendix acts as a “safe house” for beneficial gut bacteria.

Think of the colon as a wide pipe, Dr. Parker said, that may become contaminated with a pathogen such as Salmonella. Diarrhea follows, and the pipe gets repeatedly flushed, wiping everything clean, including your friendly gut microbiome. Luckily, “you’ve got this little offshoot of that pipe,” where the flow can’t really get in “because it’s so constricted,” Dr. Parker said. The friendly gut microbes can survive inside the appendix and repopulate the colon once diarrhea is over. Dr. Parker and his colleagues found that the human appendix contains a thick layer of beneficial bacteria. “They were right where we predicted they would be,” he said.

This safe house hypothesis could explain why the gut microbiome may be different in people who no longer have an appendix. In one small study, people who’d had an appendectomy had a less diverse microbiome, with a lower abundance of beneficial strains such as Butyricicoccus and Barnesiella, than did those with intact appendixes.

The appendix likely has a second function, too, Dr. Smith said: It may serve as a training camp for the immune system. “When there is an invading pathogen in the gut, it helps the GI system to mount the immune response,” she said. The human appendix is rich in special cells known as M cells. These act as scouts, detecting and capturing invasive bacteria and viruses and presenting them to the body’s defense team, such as the T lymphocytes.

If the appendix shelters beneficial bacteria and boosts immune response, that may explain its links to various diseases. According to an epidemiological study from Taiwan,patients who underwent an appendectomy have a 46% higher risk of developing irritable bowel syndrome (IBS) — a disease associated with a low abundance of Butyricicoccus bacteria. This is why, the study authors wrote, doctors should pay careful attention to people who’ve had their appendixes removed, monitoring them for potential symptoms of IBS.

The same database helped uncover other connections between appendectomy and disease. For one, there was type 2 diabetes: Within 3 years of the surgery, patients under 30 had double the risk of developing this disorder. Then there was lupus: While those who underwent appendectomy generally had higher risk for this autoimmune disease, women were particularly affected.
 

The Contentious Connections

The most heated scientific discussion surrounds the links between the appendix and conditions such as Parkinson’s disease, ulcerative colitis, and colorectal cancer. A small 2019 study showed, for example, that appendectomy may improve symptoms of certain forms of ulcerative colitis that don’t respond to standard medical treatments. A third of patients improved after their appendix was removed, and 17% fully recovered.

Why? According to Dr. Parker, appendectomy may work for ulcerative colitis because it’s “a way of suppressing the immune system, especially in the lower intestinal areas.” A 2023 meta-analysis found that people who’d had their appendix removed before being diagnosed with ulcerative colitis were less likely to need their colon removed later on.

Such a procedure may have a serious side effect, however: Colorectal cancer. French scientists discovered that removing the appendix may reduce the numbers of certain immune cells called CD3+ and CD8+ T cells, causing a weakened immune surveillance. As a result, tumor cells might escape detection.

Yet the links between appendix removal and cancer are far from clear. A recent meta-analysis found that while people with appendectomies generally had a higher risk for colorectal cancer, for Europeans, these effects were insignificant. In fact, removal of the appendix actually protected European women from this particular form of cancer. For Parker, such mixed results may stem from the fact that treatments and populations vary widely. The issue “may depend on complex social and medical factors,” Dr. Parker said.

Things also appear complicated with Parkinson’s disease — another condition linked to the appendix. A large epidemiological study showed that appendectomy is associated with a lower risk for Parkinson’s disease and a delayed age of Parkinson’s onset. It also found that a normal appendix contains α-synuclein, a protein that may accumulate in the brain and contribute to the development of Parkinson’s. “Although α-synuclein is toxic when in the brain, it appears to be quite normal when present in the appendix,” said Luis Vitetta, PhD, MD, a clinical epidemiologist at the University of Sydney, Camperdown, Australia. Yet, not all studies find that removing the appendix lowers the risk for Parkinson’s. In fact, some show the opposite results.
 

How Should Doctors View the Appendix?

Even with these mysteries and contradictions, Dr. Vitetta said, a healthy appendix in a healthy body appears to be protective. This is why, he said, when someone is diagnosed with appendicitis, careful assessment is essential before surgery is performed.

“Perhaps an antibiotic can actually help fix it,” he said. A 2020 study published in The New England Journal of Medicine showed that antibiotics may indeed be a good alternative to surgery for the treatment of appendicitis. “We don’t want necessarily to remove an appendix that could be beneficial,” Dr. Smith said.

The many links between the appendix and various diseases mean that doctors should be more vigilant when treating patients who’ve had this organ removed, Dr. Parker said. “When a patient loses an appendix, depending on their environment, there may be effects on infection and cancer. So they might need more regular checkups,” he said. This could include monitoring for IBS and colorectal cancer.

What’s more, Dr. Parker believes that research on the appendix puts even more emphasis on the need to protect the gut microbiome — such as taking probiotics with antibiotics. And while we are still a long way from understanding how exactly this worm-like structure affects various diseases, one thing appears quite certain: The appendix is not useless. “If Darwin had the information that we have, he would not have drawn these conclusions,” Dr. Parker said.
 

A version of this article first appeared on Medscape.com.

When doctors and patients consider the appendix, it’s often with urgency. In cases of appendicitis, the clock could be ticking down to a life-threatening burst. Thus, despite recent research suggesting antibiotics could be an alternative therapy, appendectomy remains standard for uncomplicated appendicitis.

But what if removing the appendix could raise the risk for gastrointestinal (GI) diseases like irritable bowel syndrome and colorectal cancer? That’s what some emerging science suggests. And though the research is early and mixed, it’s enough to give some health professionals pause.

“If there’s no reason to remove the appendix, then it’s better to have one,” said Heather Smith, PhD, a comparative anatomist at Midwestern University, Glendale, Arizona. Preemptive removal is not supported by the evidence, she said.

To be fair, we’ve come a long way since 1928, when American physician Miles Breuer, MD, suggested that people with infected appendixes should be left to perish, so as to remove their inferior DNA from the gene pool (he called such people “uncivilized” and “candidates for extinction”). Charles Darwin, while less radical, believed the appendix was at best useless — a mere vestige of our ancestors switching diets from leaves to fruits.

What we know now is that the appendix isn’t just a troublesome piece of worthless flesh. Instead, it may act as a safe house for friendly gut bacteria and a training camp for the immune system. It also appears to play a role in several medical conditions, from ulcerative colitis and colorectal cancer to Parkinson’s disease and lupus. The roughly 300,000 Americans who undergo appendectomy each year should be made aware of this, some experts say. But the frustrating truth is, scientists are still trying to figure out in which cases having an appendix is protective and in which we may be better off without it.
 

A ‘Worm’ as Intestinal Protection

The appendix is a blind pouch (meaning its ending is closed off) that extends from the large intestine. Not all mammals have one; it’s been found in several species of primates and rodents, as well as in rabbits, wombats, and Florida manatees, among others (dogs and cats don’t have it). While a human appendix “looks like a little worm,” Dr. Smith said, these anatomical structures come in various sizes and shapes. Some are thick, as in a beaver, while others are long and spiraling, like a rabbit’s.

Comparative anatomy studies reveal that the appendix has evolved independently at least 29 times throughout mammalian evolution. This suggests that “it has some kind of an adaptive function,” Dr. Smith said. When French scientists analyzed data from 258 species of mammals, they discovered that those that possess an appendix live longer than those without one. A possible explanation, the researchers wrote, may lie with the appendix’s role in preventing diarrhea.

Their 2023 study supported this hypothesis. Based on veterinary records of 45 different species of primates housed in a French zoo, the scientists established that primates with appendixes are far less likely to suffer severe diarrhea than those that don’t possess this organ. The appendix, it appears, might be our tiny weapon against bowel troubles.

For immunologist William Parker, PhD, a visiting scholar at the University of North Carolina at Chapel Hill, these data are “about as good as we could hope for” in support of the idea that the appendix might protect mammals from GI problems. An experiment on humans would be unethical, Dr. Parker said. But observational studies offer clues.

One study showed that compared with people with an intact appendix, young adults with a history of appendectomy have more than double the risk of developing a serious infection with non-typhoidal Salmonella of the kind that would require hospitalization.
 

A ‘Safe House’ for Bacteria

Such studies add weight to a theory that Dr. Parker and his colleagues developed back in 2007: That the appendix acts as a “safe house” for beneficial gut bacteria.

Think of the colon as a wide pipe, Dr. Parker said, that may become contaminated with a pathogen such as Salmonella. Diarrhea follows, and the pipe gets repeatedly flushed, wiping everything clean, including your friendly gut microbiome. Luckily, “you’ve got this little offshoot of that pipe,” where the flow can’t really get in “because it’s so constricted,” Dr. Parker said. The friendly gut microbes can survive inside the appendix and repopulate the colon once diarrhea is over. Dr. Parker and his colleagues found that the human appendix contains a thick layer of beneficial bacteria. “They were right where we predicted they would be,” he said.

This safe house hypothesis could explain why the gut microbiome may be different in people who no longer have an appendix. In one small study, people who’d had an appendectomy had a less diverse microbiome, with a lower abundance of beneficial strains such as Butyricicoccus and Barnesiella, than did those with intact appendixes.

The appendix likely has a second function, too, Dr. Smith said: It may serve as a training camp for the immune system. “When there is an invading pathogen in the gut, it helps the GI system to mount the immune response,” she said. The human appendix is rich in special cells known as M cells. These act as scouts, detecting and capturing invasive bacteria and viruses and presenting them to the body’s defense team, such as the T lymphocytes.

If the appendix shelters beneficial bacteria and boosts immune response, that may explain its links to various diseases. According to an epidemiological study from Taiwan,patients who underwent an appendectomy have a 46% higher risk of developing irritable bowel syndrome (IBS) — a disease associated with a low abundance of Butyricicoccus bacteria. This is why, the study authors wrote, doctors should pay careful attention to people who’ve had their appendixes removed, monitoring them for potential symptoms of IBS.

The same database helped uncover other connections between appendectomy and disease. For one, there was type 2 diabetes: Within 3 years of the surgery, patients under 30 had double the risk of developing this disorder. Then there was lupus: While those who underwent appendectomy generally had higher risk for this autoimmune disease, women were particularly affected.
 

The Contentious Connections

The most heated scientific discussion surrounds the links between the appendix and conditions such as Parkinson’s disease, ulcerative colitis, and colorectal cancer. A small 2019 study showed, for example, that appendectomy may improve symptoms of certain forms of ulcerative colitis that don’t respond to standard medical treatments. A third of patients improved after their appendix was removed, and 17% fully recovered.

Why? According to Dr. Parker, appendectomy may work for ulcerative colitis because it’s “a way of suppressing the immune system, especially in the lower intestinal areas.” A 2023 meta-analysis found that people who’d had their appendix removed before being diagnosed with ulcerative colitis were less likely to need their colon removed later on.

Such a procedure may have a serious side effect, however: Colorectal cancer. French scientists discovered that removing the appendix may reduce the numbers of certain immune cells called CD3+ and CD8+ T cells, causing a weakened immune surveillance. As a result, tumor cells might escape detection.

Yet the links between appendix removal and cancer are far from clear. A recent meta-analysis found that while people with appendectomies generally had a higher risk for colorectal cancer, for Europeans, these effects were insignificant. In fact, removal of the appendix actually protected European women from this particular form of cancer. For Parker, such mixed results may stem from the fact that treatments and populations vary widely. The issue “may depend on complex social and medical factors,” Dr. Parker said.

Things also appear complicated with Parkinson’s disease — another condition linked to the appendix. A large epidemiological study showed that appendectomy is associated with a lower risk for Parkinson’s disease and a delayed age of Parkinson’s onset. It also found that a normal appendix contains α-synuclein, a protein that may accumulate in the brain and contribute to the development of Parkinson’s. “Although α-synuclein is toxic when in the brain, it appears to be quite normal when present in the appendix,” said Luis Vitetta, PhD, MD, a clinical epidemiologist at the University of Sydney, Camperdown, Australia. Yet, not all studies find that removing the appendix lowers the risk for Parkinson’s. In fact, some show the opposite results.
 

How Should Doctors View the Appendix?

Even with these mysteries and contradictions, Dr. Vitetta said, a healthy appendix in a healthy body appears to be protective. This is why, he said, when someone is diagnosed with appendicitis, careful assessment is essential before surgery is performed.

“Perhaps an antibiotic can actually help fix it,” he said. A 2020 study published in The New England Journal of Medicine showed that antibiotics may indeed be a good alternative to surgery for the treatment of appendicitis. “We don’t want necessarily to remove an appendix that could be beneficial,” Dr. Smith said.

The many links between the appendix and various diseases mean that doctors should be more vigilant when treating patients who’ve had this organ removed, Dr. Parker said. “When a patient loses an appendix, depending on their environment, there may be effects on infection and cancer. So they might need more regular checkups,” he said. This could include monitoring for IBS and colorectal cancer.

What’s more, Dr. Parker believes that research on the appendix puts even more emphasis on the need to protect the gut microbiome — such as taking probiotics with antibiotics. And while we are still a long way from understanding how exactly this worm-like structure affects various diseases, one thing appears quite certain: The appendix is not useless. “If Darwin had the information that we have, he would not have drawn these conclusions,” Dr. Parker said.
 

A version of this article first appeared on Medscape.com.

When doctors and patients consider the appendix, it’s often with urgency. In cases of appendicitis, the clock could be ticking down to a life-threatening burst. Thus, despite recent research suggesting antibiotics could be an alternative therapy, appendectomy remains standard for uncomplicated appendicitis.

But what if removing the appendix could raise the risk for gastrointestinal (GI) diseases like irritable bowel syndrome and colorectal cancer? That’s what some emerging science suggests. And though the research is early and mixed, it’s enough to give some health professionals pause.

“If there’s no reason to remove the appendix, then it’s better to have one,” said Heather Smith, PhD, a comparative anatomist at Midwestern University, Glendale, Arizona. Preemptive removal is not supported by the evidence, she said.

To be fair, we’ve come a long way since 1928, when American physician Miles Breuer, MD, suggested that people with infected appendixes should be left to perish, so as to remove their inferior DNA from the gene pool (he called such people “uncivilized” and “candidates for extinction”). Charles Darwin, while less radical, believed the appendix was at best useless — a mere vestige of our ancestors switching diets from leaves to fruits.

What we know now is that the appendix isn’t just a troublesome piece of worthless flesh. Instead, it may act as a safe house for friendly gut bacteria and a training camp for the immune system. It also appears to play a role in several medical conditions, from ulcerative colitis and colorectal cancer to Parkinson’s disease and lupus. The roughly 300,000 Americans who undergo appendectomy each year should be made aware of this, some experts say. But the frustrating truth is, scientists are still trying to figure out in which cases having an appendix is protective and in which we may be better off without it.
 

A ‘Worm’ as Intestinal Protection

The appendix is a blind pouch (meaning its ending is closed off) that extends from the large intestine. Not all mammals have one; it’s been found in several species of primates and rodents, as well as in rabbits, wombats, and Florida manatees, among others (dogs and cats don’t have it). While a human appendix “looks like a little worm,” Dr. Smith said, these anatomical structures come in various sizes and shapes. Some are thick, as in a beaver, while others are long and spiraling, like a rabbit’s.

Comparative anatomy studies reveal that the appendix has evolved independently at least 29 times throughout mammalian evolution. This suggests that “it has some kind of an adaptive function,” Dr. Smith said. When French scientists analyzed data from 258 species of mammals, they discovered that those that possess an appendix live longer than those without one. A possible explanation, the researchers wrote, may lie with the appendix’s role in preventing diarrhea.

Their 2023 study supported this hypothesis. Based on veterinary records of 45 different species of primates housed in a French zoo, the scientists established that primates with appendixes are far less likely to suffer severe diarrhea than those that don’t possess this organ. The appendix, it appears, might be our tiny weapon against bowel troubles.

For immunologist William Parker, PhD, a visiting scholar at the University of North Carolina at Chapel Hill, these data are “about as good as we could hope for” in support of the idea that the appendix might protect mammals from GI problems. An experiment on humans would be unethical, Dr. Parker said. But observational studies offer clues.

One study showed that compared with people with an intact appendix, young adults with a history of appendectomy have more than double the risk of developing a serious infection with non-typhoidal Salmonella of the kind that would require hospitalization.
 

A ‘Safe House’ for Bacteria

Such studies add weight to a theory that Dr. Parker and his colleagues developed back in 2007: That the appendix acts as a “safe house” for beneficial gut bacteria.

Think of the colon as a wide pipe, Dr. Parker said, that may become contaminated with a pathogen such as Salmonella. Diarrhea follows, and the pipe gets repeatedly flushed, wiping everything clean, including your friendly gut microbiome. Luckily, “you’ve got this little offshoot of that pipe,” where the flow can’t really get in “because it’s so constricted,” Dr. Parker said. The friendly gut microbes can survive inside the appendix and repopulate the colon once diarrhea is over. Dr. Parker and his colleagues found that the human appendix contains a thick layer of beneficial bacteria. “They were right where we predicted they would be,” he said.

This safe house hypothesis could explain why the gut microbiome may be different in people who no longer have an appendix. In one small study, people who’d had an appendectomy had a less diverse microbiome, with a lower abundance of beneficial strains such as Butyricicoccus and Barnesiella, than did those with intact appendixes.

The appendix likely has a second function, too, Dr. Smith said: It may serve as a training camp for the immune system. “When there is an invading pathogen in the gut, it helps the GI system to mount the immune response,” she said. The human appendix is rich in special cells known as M cells. These act as scouts, detecting and capturing invasive bacteria and viruses and presenting them to the body’s defense team, such as the T lymphocytes.

If the appendix shelters beneficial bacteria and boosts immune response, that may explain its links to various diseases. According to an epidemiological study from Taiwan,patients who underwent an appendectomy have a 46% higher risk of developing irritable bowel syndrome (IBS) — a disease associated with a low abundance of Butyricicoccus bacteria. This is why, the study authors wrote, doctors should pay careful attention to people who’ve had their appendixes removed, monitoring them for potential symptoms of IBS.

The same database helped uncover other connections between appendectomy and disease. For one, there was type 2 diabetes: Within 3 years of the surgery, patients under 30 had double the risk of developing this disorder. Then there was lupus: While those who underwent appendectomy generally had higher risk for this autoimmune disease, women were particularly affected.
 

The Contentious Connections

The most heated scientific discussion surrounds the links between the appendix and conditions such as Parkinson’s disease, ulcerative colitis, and colorectal cancer. A small 2019 study showed, for example, that appendectomy may improve symptoms of certain forms of ulcerative colitis that don’t respond to standard medical treatments. A third of patients improved after their appendix was removed, and 17% fully recovered.

Why? According to Dr. Parker, appendectomy may work for ulcerative colitis because it’s “a way of suppressing the immune system, especially in the lower intestinal areas.” A 2023 meta-analysis found that people who’d had their appendix removed before being diagnosed with ulcerative colitis were less likely to need their colon removed later on.

Such a procedure may have a serious side effect, however: Colorectal cancer. French scientists discovered that removing the appendix may reduce the numbers of certain immune cells called CD3+ and CD8+ T cells, causing a weakened immune surveillance. As a result, tumor cells might escape detection.

Yet the links between appendix removal and cancer are far from clear. A recent meta-analysis found that while people with appendectomies generally had a higher risk for colorectal cancer, for Europeans, these effects were insignificant. In fact, removal of the appendix actually protected European women from this particular form of cancer. For Parker, such mixed results may stem from the fact that treatments and populations vary widely. The issue “may depend on complex social and medical factors,” Dr. Parker said.

Things also appear complicated with Parkinson’s disease — another condition linked to the appendix. A large epidemiological study showed that appendectomy is associated with a lower risk for Parkinson’s disease and a delayed age of Parkinson’s onset. It also found that a normal appendix contains α-synuclein, a protein that may accumulate in the brain and contribute to the development of Parkinson’s. “Although α-synuclein is toxic when in the brain, it appears to be quite normal when present in the appendix,” said Luis Vitetta, PhD, MD, a clinical epidemiologist at the University of Sydney, Camperdown, Australia. Yet, not all studies find that removing the appendix lowers the risk for Parkinson’s. In fact, some show the opposite results.
 

How Should Doctors View the Appendix?

Even with these mysteries and contradictions, Dr. Vitetta said, a healthy appendix in a healthy body appears to be protective. This is why, he said, when someone is diagnosed with appendicitis, careful assessment is essential before surgery is performed.

“Perhaps an antibiotic can actually help fix it,” he said. A 2020 study published in The New England Journal of Medicine showed that antibiotics may indeed be a good alternative to surgery for the treatment of appendicitis. “We don’t want necessarily to remove an appendix that could be beneficial,” Dr. Smith said.

The many links between the appendix and various diseases mean that doctors should be more vigilant when treating patients who’ve had this organ removed, Dr. Parker said. “When a patient loses an appendix, depending on their environment, there may be effects on infection and cancer. So they might need more regular checkups,” he said. This could include monitoring for IBS and colorectal cancer.

What’s more, Dr. Parker believes that research on the appendix puts even more emphasis on the need to protect the gut microbiome — such as taking probiotics with antibiotics. And while we are still a long way from understanding how exactly this worm-like structure affects various diseases, one thing appears quite certain: The appendix is not useless. “If Darwin had the information that we have, he would not have drawn these conclusions,” Dr. Parker said.
 

A version of this article first appeared on Medscape.com.

CHICAGO — Genetics and diet have been among the top theories for what may be fueling the troubling rise of colorectal cancer in young adults. Now, an early look at genetic data from people with colorectal cancer further suggests that the cause is linked to what is happening in the gut.

The findings were presented at the annual meeting of the American Society for Clinical Oncology (ASCO) by researchers from Ohio State University. For the analysis, they analyzed genetic data on tumors.

The researchers found signs that a high-fat, low-fiber diet may increase inflammation in the gut that prevents it from naturally suppressing tumors. The cells of young people with colorectal cancer also appeared to have aged more quickly — by 15 years on average — than a person’s actual age. That’s unusual, because older people with colorectal cancer don’t have the same boost in cellular aging.

The rate of colorectal cancer among young people has been rising at an alarming rate, according to a 2023 report from the American Cancer Society. In 2019, one in five colorectal cancer cases were among people younger than 55. That’s up from 1 in 10 in 1995, which means the rate has doubled in less than 30 years.
 

Need Colon Cancer Screening?

Who needs a colorectal cancer screening? Ask colorectal cancer specialist Nancy Kemeny, MD.

A 2017 analysis estimated that a person’s risk of colorectal cancer increased 12% by eating 3.5 ounces of red or processed meat daily, which is the equivalent of the size of a deck of playing cards. The same study also linked colorectal cancer risk to alcohol intake, citing its ethanol content. Eating a diet high in fiber can reduce a person’s risk.

This latest study aligned with previous findings that link bacteria called Fusobacterium to colorectal cancer. It’s not unusual for Fusobacterium to be present in a person’s mouth, but it is more likely to be found in the intestines of colorectal cancer patients, compared with those of healthy people. One study even found that people with colorectal cancer were five times more likely to have Fusobacterium in their stool, compared with healthy people.

Colorectal cancer is more common among men than women, “likely reflecting differences in risk factor prevalence, such as excess body weight and processed meat consumption,” the authors of the 2023 American Cancer Society report explained.

People younger than 45 should alert their medical provider if they have constipation, rectal bleeding, or sudden changes in bowel movements, which can be symptoms of colorectal cancer. Screening for colorectal cancer should begin for most people at age 45.

A version of this article appeared on WebMD.com.

CHICAGO — Genetics and diet have been among the top theories for what may be fueling the troubling rise of colorectal cancer in young adults. Now, an early look at genetic data from people with colorectal cancer further suggests that the cause is linked to what is happening in the gut.

The findings were presented at the annual meeting of the American Society for Clinical Oncology (ASCO) by researchers from Ohio State University. For the analysis, they analyzed genetic data on tumors.

The researchers found signs that a high-fat, low-fiber diet may increase inflammation in the gut that prevents it from naturally suppressing tumors. The cells of young people with colorectal cancer also appeared to have aged more quickly — by 15 years on average — than a person’s actual age. That’s unusual, because older people with colorectal cancer don’t have the same boost in cellular aging.

The rate of colorectal cancer among young people has been rising at an alarming rate, according to a 2023 report from the American Cancer Society. In 2019, one in five colorectal cancer cases were among people younger than 55. That’s up from 1 in 10 in 1995, which means the rate has doubled in less than 30 years.
 

Need Colon Cancer Screening?

Who needs a colorectal cancer screening? Ask colorectal cancer specialist Nancy Kemeny, MD.

A 2017 analysis estimated that a person’s risk of colorectal cancer increased 12% by eating 3.5 ounces of red or processed meat daily, which is the equivalent of the size of a deck of playing cards. The same study also linked colorectal cancer risk to alcohol intake, citing its ethanol content. Eating a diet high in fiber can reduce a person’s risk.

This latest study aligned with previous findings that link bacteria called Fusobacterium to colorectal cancer. It’s not unusual for Fusobacterium to be present in a person’s mouth, but it is more likely to be found in the intestines of colorectal cancer patients, compared with those of healthy people. One study even found that people with colorectal cancer were five times more likely to have Fusobacterium in their stool, compared with healthy people.

Colorectal cancer is more common among men than women, “likely reflecting differences in risk factor prevalence, such as excess body weight and processed meat consumption,” the authors of the 2023 American Cancer Society report explained.

People younger than 45 should alert their medical provider if they have constipation, rectal bleeding, or sudden changes in bowel movements, which can be symptoms of colorectal cancer. Screening for colorectal cancer should begin for most people at age 45.

A version of this article appeared on WebMD.com.

CHICAGO — Genetics and diet have been among the top theories for what may be fueling the troubling rise of colorectal cancer in young adults. Now, an early look at genetic data from people with colorectal cancer further suggests that the cause is linked to what is happening in the gut.

The findings were presented at the annual meeting of the American Society for Clinical Oncology (ASCO) by researchers from Ohio State University. For the analysis, they analyzed genetic data on tumors.

The researchers found signs that a high-fat, low-fiber diet may increase inflammation in the gut that prevents it from naturally suppressing tumors. The cells of young people with colorectal cancer also appeared to have aged more quickly — by 15 years on average — than a person’s actual age. That’s unusual, because older people with colorectal cancer don’t have the same boost in cellular aging.

The rate of colorectal cancer among young people has been rising at an alarming rate, according to a 2023 report from the American Cancer Society. In 2019, one in five colorectal cancer cases were among people younger than 55. That’s up from 1 in 10 in 1995, which means the rate has doubled in less than 30 years.
 

Need Colon Cancer Screening?

Who needs a colorectal cancer screening? Ask colorectal cancer specialist Nancy Kemeny, MD.

A 2017 analysis estimated that a person’s risk of colorectal cancer increased 12% by eating 3.5 ounces of red or processed meat daily, which is the equivalent of the size of a deck of playing cards. The same study also linked colorectal cancer risk to alcohol intake, citing its ethanol content. Eating a diet high in fiber can reduce a person’s risk.

This latest study aligned with previous findings that link bacteria called Fusobacterium to colorectal cancer. It’s not unusual for Fusobacterium to be present in a person’s mouth, but it is more likely to be found in the intestines of colorectal cancer patients, compared with those of healthy people. One study even found that people with colorectal cancer were five times more likely to have Fusobacterium in their stool, compared with healthy people.

Colorectal cancer is more common among men than women, “likely reflecting differences in risk factor prevalence, such as excess body weight and processed meat consumption,” the authors of the 2023 American Cancer Society report explained.

People younger than 45 should alert their medical provider if they have constipation, rectal bleeding, or sudden changes in bowel movements, which can be symptoms of colorectal cancer. Screening for colorectal cancer should begin for most people at age 45.

A version of this article appeared on WebMD.com.

TOPLINE:

Patients with early-onset colorectal cancer (EOCRC) often present with hematochezia or abdominal pain, symptoms frequently overlooked in younger populations, leading to delays in diagnosis of 4-6 months, a new analysis showed.

METHODOLOGY:

• As the number of cases of EOCRC, defined as colorectal cancer (CRC) diagnosed before age 50, continues to rise, early detection has become increasingly important. Improved recognition of presenting signs and symptoms associated with EOCRC could lead to a more timely diagnosis and better clinical outcomes.
• In a systematic review and meta-analysis of 81 studies with 24.9 million EOCRC cases, researchers sought to determine the most common presenting signs and symptoms, their association with EOCRC risk, and the time from presentation to diagnosis.
• Data extraction and quality assessment were performed independently in duplicate using PRISMA guidelines, and Joanna Briggs Institute critical appraisal tools were used to measure the risk of bias.

TAKEAWAY:

• Hematochezia was the most common presenting sign/symptom, with a pooled prevalence of 45%, followed by abdominal pain, with a pooled prevalence of 40%.
• Altered bowel habits, which included constipation, diarrhea, and alternating bowel habits, were the third most common presenting sign/symptom (pooled prevalence of 27%), followed by unexplained weight loss (pooled prevalence of 17%).
• The likelihood of EOCRC was estimated to be fivefold to 54-fold higher with hematochezia and 1.3-fold to sixfold higher with abdominal pain.
• The mean time from sign or symptom onset to EOCRC diagnosis was 6.4 months (range, 1.8-13.7 months).

IN PRACTICE:

“These findings and the increasing risk of CRC in individuals younger than 50 years highlight the urgent need to educate clinicians and patients about these signs and symptoms to ensure that diagnostic workup and resolution are not delayed. Adapting current clinical practice to identify and address these signs and symptoms through careful clinical triage and follow-up could help limit morbidity and mortality associated with EOCRC,” the authors wrote.

SOURCE:

The study, with Joshua Demb, PhD, MPH, division of gastroenterology, department of medicine, University of California, San Diego, was published online May 24 in JAMA Network Open.

LIMITATIONS:

Significant heterogeneity across studies affected the ability to meta-analyze some results. The cross-sectional data limited the ability to stratify by age, sex, race and ethnicity, or genetic ancestry. It was not possible to evaluate the impact of time to diagnosis on CRC outcomes due to a limited number of studies answering this question. Researchers were unable to examine the constellation of signs and symptoms because they lacked individual-level data from each study.

DISCLOSURES:

The authors disclosed no relevant conflicts of interest. No specific funding was disclosed.
 

A version of this article appeared on Medscape.com.

TOPLINE:

Patients with early-onset colorectal cancer (EOCRC) often present with hematochezia or abdominal pain, symptoms frequently overlooked in younger populations, leading to delays in diagnosis of 4-6 months, a new analysis showed.

METHODOLOGY:

• As the number of cases of EOCRC, defined as colorectal cancer (CRC) diagnosed before age 50, continues to rise, early detection has become increasingly important. Improved recognition of presenting signs and symptoms associated with EOCRC could lead to a more timely diagnosis and better clinical outcomes.
• In a systematic review and meta-analysis of 81 studies with 24.9 million EOCRC cases, researchers sought to determine the most common presenting signs and symptoms, their association with EOCRC risk, and the time from presentation to diagnosis.
• Data extraction and quality assessment were performed independently in duplicate using PRISMA guidelines, and Joanna Briggs Institute critical appraisal tools were used to measure the risk of bias.

TAKEAWAY:

• Hematochezia was the most common presenting sign/symptom, with a pooled prevalence of 45%, followed by abdominal pain, with a pooled prevalence of 40%.
• Altered bowel habits, which included constipation, diarrhea, and alternating bowel habits, were the third most common presenting sign/symptom (pooled prevalence of 27%), followed by unexplained weight loss (pooled prevalence of 17%).
• The likelihood of EOCRC was estimated to be fivefold to 54-fold higher with hematochezia and 1.3-fold to sixfold higher with abdominal pain.
• The mean time from sign or symptom onset to EOCRC diagnosis was 6.4 months (range, 1.8-13.7 months).

IN PRACTICE:

“These findings and the increasing risk of CRC in individuals younger than 50 years highlight the urgent need to educate clinicians and patients about these signs and symptoms to ensure that diagnostic workup and resolution are not delayed. Adapting current clinical practice to identify and address these signs and symptoms through careful clinical triage and follow-up could help limit morbidity and mortality associated with EOCRC,” the authors wrote.

SOURCE:

The study, with Joshua Demb, PhD, MPH, division of gastroenterology, department of medicine, University of California, San Diego, was published online May 24 in JAMA Network Open.

LIMITATIONS:

Significant heterogeneity across studies affected the ability to meta-analyze some results. The cross-sectional data limited the ability to stratify by age, sex, race and ethnicity, or genetic ancestry. It was not possible to evaluate the impact of time to diagnosis on CRC outcomes due to a limited number of studies answering this question. Researchers were unable to examine the constellation of signs and symptoms because they lacked individual-level data from each study.

DISCLOSURES:

The authors disclosed no relevant conflicts of interest. No specific funding was disclosed.
 

A version of this article appeared on Medscape.com.

TOPLINE:

Patients with early-onset colorectal cancer (EOCRC) often present with hematochezia or abdominal pain, symptoms frequently overlooked in younger populations, leading to delays in diagnosis of 4-6 months, a new analysis showed.

METHODOLOGY:

• As the number of cases of EOCRC, defined as colorectal cancer (CRC) diagnosed before age 50, continues to rise, early detection has become increasingly important. Improved recognition of presenting signs and symptoms associated with EOCRC could lead to a more timely diagnosis and better clinical outcomes.
• In a systematic review and meta-analysis of 81 studies with 24.9 million EOCRC cases, researchers sought to determine the most common presenting signs and symptoms, their association with EOCRC risk, and the time from presentation to diagnosis.
• Data extraction and quality assessment were performed independently in duplicate using PRISMA guidelines, and Joanna Briggs Institute critical appraisal tools were used to measure the risk of bias.

TAKEAWAY:

• Hematochezia was the most common presenting sign/symptom, with a pooled prevalence of 45%, followed by abdominal pain, with a pooled prevalence of 40%.
• Altered bowel habits, which included constipation, diarrhea, and alternating bowel habits, were the third most common presenting sign/symptom (pooled prevalence of 27%), followed by unexplained weight loss (pooled prevalence of 17%).
• The likelihood of EOCRC was estimated to be fivefold to 54-fold higher with hematochezia and 1.3-fold to sixfold higher with abdominal pain.
• The mean time from sign or symptom onset to EOCRC diagnosis was 6.4 months (range, 1.8-13.7 months).

IN PRACTICE:

“These findings and the increasing risk of CRC in individuals younger than 50 years highlight the urgent need to educate clinicians and patients about these signs and symptoms to ensure that diagnostic workup and resolution are not delayed. Adapting current clinical practice to identify and address these signs and symptoms through careful clinical triage and follow-up could help limit morbidity and mortality associated with EOCRC,” the authors wrote.

SOURCE:

The study, with Joshua Demb, PhD, MPH, division of gastroenterology, department of medicine, University of California, San Diego, was published online May 24 in JAMA Network Open.

LIMITATIONS:

Significant heterogeneity across studies affected the ability to meta-analyze some results. The cross-sectional data limited the ability to stratify by age, sex, race and ethnicity, or genetic ancestry. It was not possible to evaluate the impact of time to diagnosis on CRC outcomes due to a limited number of studies answering this question. Researchers were unable to examine the constellation of signs and symptoms because they lacked individual-level data from each study.

DISCLOSURES:

The authors disclosed no relevant conflicts of interest. No specific funding was disclosed.
 

A version of this article appeared on Medscape.com.

WASHINGTON — Eating within 3 hours of bedtime at least 4 days a week could increase chances for developing colorectal cancer, according to the results of research presented at the annual Digestive Disease Week^® (DDW).

Investigators in a new study questioned 664 people getting a colonoscopy to screen for cancer, and 42% said they were late eaters. This group was 46% more likely than non–late eaters to have an adenoma found during colonoscopy. An estimated 5% to 10% of them become cancerous over time.

“A lot of other studies are about what we eat but not when we eat,” said Edena Khoshaba, lead investigator and a medical student at Rush University Medical College in Chicago. “The common advice includes not eating red meat, eating more fruits and vegetables — which is great, of course — but we wanted to see if the timing affects us at all.”

Ms. Khoshaba and colleagues found it did. Late eaters were 5.5 times more likely to have three or more tubular adenomas compared to non–late eaters, even after adjusting for what people were eating. Tubular adenomas are the most common type of polyp found in the colon.

So, what’s the possible connection between late eating and the risk for colorectal cancer?
 

Resetting Your Internal Clock

Eating close to bedtime could be throwing off the body’s circadian rhythm. But in this case, it’s not the central circadian center located in the brain — the one that releases melatonin. Instead, late eating could disrupt the peripheral circadian rhythm, part of which is found in the GI tract. For example, if a person is eating late at night, the brain thinks it is nighttime while the gut thinks it is daytime, Ms. Khoshaba said in an interview.

This is an interesting study, said Amy Bragagnini, MS, RD, spokesperson for the Academy of Nutrition and Dietetics, when asked to comment on the research. “It is true that eating later at night can disrupt your circadian rhythm.”

“In addition, many of my patients have told me that when they do eat later at night, they don’t always make the healthiest food choices,” Ms. Bragagnini said. “Their late-night food choices are generally higher in added sugar and fat. This may cause them to consume far more calories than their body needs.” So, eating late at night can also lead to unwanted weight gain.

An unanswered question is if late eating is connected in any way at all to increasing rates of colorectal cancer seen in younger patients.

This was an observational study, and another possible limitation, Ms. Khoshaba said, is that people were asked to recall their diets over 24 hours, which may not always be accurate.

Some of the organisms in the gut have their own internal clocks that follow a daily rhythm, and what someone eat determines how many different kinds of these organisms are active, Ms. Bragagnini said.

“So, if your late-night eating consists of foods high in sugar and fat, you may be negatively impacting your microbiome.” she said.

The next step for Ms. Khoshaba and colleagues is a study examining the peripheral circadian rhythm, changes in the gut microbiome, and the risk for developing metabolic syndrome. Ms. Khoshaba and Ms. Bragagnini had no relevant disclosures.

A version of this article appeared on Medscape.com.

WASHINGTON — Eating within 3 hours of bedtime at least 4 days a week could increase chances for developing colorectal cancer, according to the results of research presented at the annual Digestive Disease Week^® (DDW).

Investigators in a new study questioned 664 people getting a colonoscopy to screen for cancer, and 42% said they were late eaters. This group was 46% more likely than non–late eaters to have an adenoma found during colonoscopy. An estimated 5% to 10% of them become cancerous over time.

“A lot of other studies are about what we eat but not when we eat,” said Edena Khoshaba, lead investigator and a medical student at Rush University Medical College in Chicago. “The common advice includes not eating red meat, eating more fruits and vegetables — which is great, of course — but we wanted to see if the timing affects us at all.”

Ms. Khoshaba and colleagues found it did. Late eaters were 5.5 times more likely to have three or more tubular adenomas compared to non–late eaters, even after adjusting for what people were eating. Tubular adenomas are the most common type of polyp found in the colon.

So, what’s the possible connection between late eating and the risk for colorectal cancer?
 

Resetting Your Internal Clock

Eating close to bedtime could be throwing off the body’s circadian rhythm. But in this case, it’s not the central circadian center located in the brain — the one that releases melatonin. Instead, late eating could disrupt the peripheral circadian rhythm, part of which is found in the GI tract. For example, if a person is eating late at night, the brain thinks it is nighttime while the gut thinks it is daytime, Ms. Khoshaba said in an interview.

This is an interesting study, said Amy Bragagnini, MS, RD, spokesperson for the Academy of Nutrition and Dietetics, when asked to comment on the research. “It is true that eating later at night can disrupt your circadian rhythm.”

“In addition, many of my patients have told me that when they do eat later at night, they don’t always make the healthiest food choices,” Ms. Bragagnini said. “Their late-night food choices are generally higher in added sugar and fat. This may cause them to consume far more calories than their body needs.” So, eating late at night can also lead to unwanted weight gain.

An unanswered question is if late eating is connected in any way at all to increasing rates of colorectal cancer seen in younger patients.

This was an observational study, and another possible limitation, Ms. Khoshaba said, is that people were asked to recall their diets over 24 hours, which may not always be accurate.

Some of the organisms in the gut have their own internal clocks that follow a daily rhythm, and what someone eat determines how many different kinds of these organisms are active, Ms. Bragagnini said.

“So, if your late-night eating consists of foods high in sugar and fat, you may be negatively impacting your microbiome.” she said.

The next step for Ms. Khoshaba and colleagues is a study examining the peripheral circadian rhythm, changes in the gut microbiome, and the risk for developing metabolic syndrome. Ms. Khoshaba and Ms. Bragagnini had no relevant disclosures.

A version of this article appeared on Medscape.com.

WASHINGTON — Eating within 3 hours of bedtime at least 4 days a week could increase chances for developing colorectal cancer, according to the results of research presented at the annual Digestive Disease Week^® (DDW).

Investigators in a new study questioned 664 people getting a colonoscopy to screen for cancer, and 42% said they were late eaters. This group was 46% more likely than non–late eaters to have an adenoma found during colonoscopy. An estimated 5% to 10% of them become cancerous over time.

“A lot of other studies are about what we eat but not when we eat,” said Edena Khoshaba, lead investigator and a medical student at Rush University Medical College in Chicago. “The common advice includes not eating red meat, eating more fruits and vegetables — which is great, of course — but we wanted to see if the timing affects us at all.”

Ms. Khoshaba and colleagues found it did. Late eaters were 5.5 times more likely to have three or more tubular adenomas compared to non–late eaters, even after adjusting for what people were eating. Tubular adenomas are the most common type of polyp found in the colon.

So, what’s the possible connection between late eating and the risk for colorectal cancer?
 

Resetting Your Internal Clock

Eating close to bedtime could be throwing off the body’s circadian rhythm. But in this case, it’s not the central circadian center located in the brain — the one that releases melatonin. Instead, late eating could disrupt the peripheral circadian rhythm, part of which is found in the GI tract. For example, if a person is eating late at night, the brain thinks it is nighttime while the gut thinks it is daytime, Ms. Khoshaba said in an interview.

This is an interesting study, said Amy Bragagnini, MS, RD, spokesperson for the Academy of Nutrition and Dietetics, when asked to comment on the research. “It is true that eating later at night can disrupt your circadian rhythm.”

“In addition, many of my patients have told me that when they do eat later at night, they don’t always make the healthiest food choices,” Ms. Bragagnini said. “Their late-night food choices are generally higher in added sugar and fat. This may cause them to consume far more calories than their body needs.” So, eating late at night can also lead to unwanted weight gain.

An unanswered question is if late eating is connected in any way at all to increasing rates of colorectal cancer seen in younger patients.

This was an observational study, and another possible limitation, Ms. Khoshaba said, is that people were asked to recall their diets over 24 hours, which may not always be accurate.

Some of the organisms in the gut have their own internal clocks that follow a daily rhythm, and what someone eat determines how many different kinds of these organisms are active, Ms. Bragagnini said.

“So, if your late-night eating consists of foods high in sugar and fat, you may be negatively impacting your microbiome.” she said.

The next step for Ms. Khoshaba and colleagues is a study examining the peripheral circadian rhythm, changes in the gut microbiome, and the risk for developing metabolic syndrome. Ms. Khoshaba and Ms. Bragagnini had no relevant disclosures.

A version of this article appeared on Medscape.com.

TOPLINE:

The recommended 10-year interval between screening colonoscopies may be safely extended to 15 years in adults with no family history of colorectal cancer (CRC) whose first colonoscopy is negative for CRC, a population-based study suggests.

METHODOLOGY:

• Using Swedish nationwide registry data, researchers compared 110,074 individuals who had a first colonoscopy with negative findings for CRC at age 45-69 years (exposed group) with more than 1.9 million matched controls who either did not have a colonoscopy during the study period or underwent colonoscopy that led to a CRC diagnosis.
• They calculated 10-year standardized incidence ratio (SIR) and standardized mortality ratio (SMR) to compare risks for CRC and CRC-specific death in the exposed and control groups based on different follow-up screening intervals.

TAKEAWAY:

• During up to 29 years of follow-up, 484 incident CRCs and 112 CRC deaths occurred in the group with a negative initial colonoscopy.
• Up to 15 years after negative colonoscopy, the 10-year cumulative risk for CRC and CRC mortality was lower than in the control group, with an SIR of 0.72 and SMR of 0.55, respectively.
• Extending the screening interval from 10 to 15 years would miss early detection of only two CRC cases and prevention of only one CRC death per 1000 individuals, while potentially avoiding 1000 colonoscopies.

IN PRACTICE:

“This study provides evidence for recommending a longer colonoscopy screening interval than what is currently recommended in most guidelines for populations with no familial risk of CRC,” the authors wrote. “A longer interval between colonoscopy screenings could be beneficial in avoiding unnecessary invasive examinations.”

SOURCE:

The study, with first author Qunfeng Liang, MSc, with the German Cancer Research Center, Heidelberg, Germany, was published online on May 2 in JAMA Oncology.

LIMITATIONS:

The study population primarily included White individuals, particularly ethnic Swedish individuals, so external validation would be necessary to generalize the recommendation to other populations. The researchers lacked data on non-endoscopic tests, such as fecal occult blood tests, which could have been performed as a substitution for colonoscopy during the interval between colonoscopy screenings.

DISCLOSURES:

The study had no specific funding. The authors had no relevant conflicts of interest.

A version of this article appeared on Medscape.com.

TOPLINE:

The recommended 10-year interval between screening colonoscopies may be safely extended to 15 years in adults with no family history of colorectal cancer (CRC) whose first colonoscopy is negative for CRC, a population-based study suggests.

METHODOLOGY:

• Using Swedish nationwide registry data, researchers compared 110,074 individuals who had a first colonoscopy with negative findings for CRC at age 45-69 years (exposed group) with more than 1.9 million matched controls who either did not have a colonoscopy during the study period or underwent colonoscopy that led to a CRC diagnosis.
• They calculated 10-year standardized incidence ratio (SIR) and standardized mortality ratio (SMR) to compare risks for CRC and CRC-specific death in the exposed and control groups based on different follow-up screening intervals.

TAKEAWAY:

• During up to 29 years of follow-up, 484 incident CRCs and 112 CRC deaths occurred in the group with a negative initial colonoscopy.
• Up to 15 years after negative colonoscopy, the 10-year cumulative risk for CRC and CRC mortality was lower than in the control group, with an SIR of 0.72 and SMR of 0.55, respectively.
• Extending the screening interval from 10 to 15 years would miss early detection of only two CRC cases and prevention of only one CRC death per 1000 individuals, while potentially avoiding 1000 colonoscopies.

IN PRACTICE:

“This study provides evidence for recommending a longer colonoscopy screening interval than what is currently recommended in most guidelines for populations with no familial risk of CRC,” the authors wrote. “A longer interval between colonoscopy screenings could be beneficial in avoiding unnecessary invasive examinations.”

SOURCE:

The study, with first author Qunfeng Liang, MSc, with the German Cancer Research Center, Heidelberg, Germany, was published online on May 2 in JAMA Oncology.

LIMITATIONS:

The study population primarily included White individuals, particularly ethnic Swedish individuals, so external validation would be necessary to generalize the recommendation to other populations. The researchers lacked data on non-endoscopic tests, such as fecal occult blood tests, which could have been performed as a substitution for colonoscopy during the interval between colonoscopy screenings.

DISCLOSURES:

The study had no specific funding. The authors had no relevant conflicts of interest.

A version of this article appeared on Medscape.com.

TOPLINE:

The recommended 10-year interval between screening colonoscopies may be safely extended to 15 years in adults with no family history of colorectal cancer (CRC) whose first colonoscopy is negative for CRC, a population-based study suggests.

METHODOLOGY:

• Using Swedish nationwide registry data, researchers compared 110,074 individuals who had a first colonoscopy with negative findings for CRC at age 45-69 years (exposed group) with more than 1.9 million matched controls who either did not have a colonoscopy during the study period or underwent colonoscopy that led to a CRC diagnosis.
• They calculated 10-year standardized incidence ratio (SIR) and standardized mortality ratio (SMR) to compare risks for CRC and CRC-specific death in the exposed and control groups based on different follow-up screening intervals.

TAKEAWAY:

• During up to 29 years of follow-up, 484 incident CRCs and 112 CRC deaths occurred in the group with a negative initial colonoscopy.
• Up to 15 years after negative colonoscopy, the 10-year cumulative risk for CRC and CRC mortality was lower than in the control group, with an SIR of 0.72 and SMR of 0.55, respectively.
• Extending the screening interval from 10 to 15 years would miss early detection of only two CRC cases and prevention of only one CRC death per 1000 individuals, while potentially avoiding 1000 colonoscopies.

IN PRACTICE:

“This study provides evidence for recommending a longer colonoscopy screening interval than what is currently recommended in most guidelines for populations with no familial risk of CRC,” the authors wrote. “A longer interval between colonoscopy screenings could be beneficial in avoiding unnecessary invasive examinations.”

SOURCE:

The study, with first author Qunfeng Liang, MSc, with the German Cancer Research Center, Heidelberg, Germany, was published online on May 2 in JAMA Oncology.

LIMITATIONS:

The study population primarily included White individuals, particularly ethnic Swedish individuals, so external validation would be necessary to generalize the recommendation to other populations. The researchers lacked data on non-endoscopic tests, such as fecal occult blood tests, which could have been performed as a substitution for colonoscopy during the interval between colonoscopy screenings.

DISCLOSURES:

The study had no specific funding. The authors had no relevant conflicts of interest.

A version of this article appeared on Medscape.com.

A contentious scientific debate is clouding prospects for a deeper understanding of the microbiome’s role in cancer, a relatively young field of research that some believe could lead to breakthroughs in the diagnosis and treatment of the second-leading cause of death in the United States. 

Last year, the controversy heightened when experts questioned a high-profile study — a 2020 analysis claiming that the tumors of 33 different cancers had their own unique microbiomes — on whether the “signature” of these bacterial compositions could help diagnose cancer.

The incident renewed the spotlight on “tumor microbiomes” because of the bold claims of the original paper and the strongly worded refutations of those claims. The broader field has focused primarily on ways the body’s microbiome interacts with cancers and cancer treatment.

This controversy has highlighted the challenges of making headway in a field where researchers may not even have the tools yet to puzzle-out the wide-ranging implications the microbiome holds for cancer diagnosis and treatment.

But it is also part of a provocative question within that larger field: whether tumors in the body, far from the natural microbiome in the gut, have their own thriving communities of bacteria, viruses, and fungi. And, if they do, how do those tumor microbiomes affect the development and progression of the cancer and the effectiveness of cancer therapies? 
 

Cancer Controversy

The evidence is undeniable that some microbes can directly cause certain cancers and that the human gut microbiome can influence the effectiveness of certain therapies. Beyond that established science, however, the research has raised as many questions as answers about what we do and don’t know about microbiota and cancer.

The only confirmed microbiomes are on the skin and in the gut, mouth, and vagina, which are all areas with an easy direct route for bacteria to enter and grow in or on the body. A series of papers in recent years have suggested that other internal organs, and tumors within them, may have their own microbiomes. 

“Whether microbes exist in tumors of internal organs beyond body surfaces exposed to the environment is a different matter,” said Ivan Vujkovic-Cvijin, PhD, an assistant professor of biomedical sciences and gastroenterology at Cedars-Sinai Medical Center in Los Angeles, whose lab studies how human gut microbes affect inflammatory diseases. “We’ve only recently had the tools to study that question on a molecular level, and the reported results have been conflicting.” 

For example, research allegedly identified microbiota in the human placenta nearly one decade ago. But subsequent research contradicted those claims and showed that the source of the “placental microbiome” was actually contamination. Subsequent similar studies for other parts of the body faced the same scrutiny and, often, eventual debunking.

“Most likely, our immune system has undergone selective pressure to eliminate everything that crosses the gut barrier because there’s not much benefit to the body to have bacteria run amok in our internal organs,” Dr. Vujkovic-Cvijin said. “That can only disrupt the functioning of our tissues, to have an external organism living inside them.” 

The controversy that erupted last summer, surrounding research from the lab of Rob Knight, PhD, at the University of California, San Diego, centered on a slightly different but related question: Could tumors harbor their own microbiomes?

This news organization spoke with two of the authors who published a paper contesting Dr. Knight’s findings: Steven Salzberg, PhD, a professor of biomedical engineering at John Hopkins Medicine, Baltimore, Maryland, and Abraham Gihawi, PhD, a research fellow at Norwich Medical School at the University of East Anglia in the United Kingdom. 

Dr. Salzberg described two major problems with Dr. Knight’s study. 

“What they found were false positives because of contamination in the database and flaws in their methods,” Dr. Salzberg said. “I can’t prove there’s no cancer microbiome, but I can say the cancer microbiomes that they reported don’t exist because the species they were finding aren’t there.”

Dr. Knight disagrees with Dr. Salzberg’s findings, noting that Dr. Salzberg and his co-authors did not examine the publicly available databases used in his study. In a written response, he said that his team’s examination of the database revealed that less than 1% of the microbial genomes overlapped with human ones and that removing them did not change their findings.

Dr. Knight also noted that his team could still “distinguish cancer types by their microbiome” even after running their analysis without the technique that Dr. Salzberg found fault with.

Dr. Salzberg said that the database linked above is not the one Dr. Knight’s study used, however. “The primary database in their study was never made public (it’s too large, they said), and it has/had about 69,000 genomes,” Dr. Salzberg said by email. “But even if we did, this is irrelevant. He’s trying to distract from the primary errors in their study,” which Dr. Salzberg said Dr. Knight’s team has not addressed. 

The critiques Dr. Salzberg raised have been leveled at other studies investigating microbiomes specifically within tumors and independent of the body’s microbiome.

For example, a 2019 study in Nature described a fungal microbiome in pancreatic cancer that a Nature paper 4 years later directly contradicted, citing flaws that invalidated the original findings. A different 2019 study in Cell examined pancreatic tumor microbiota and patient outcomes, but it’s unclear whether the microorganisms moved from the gut to the pancreas or “constitute a durably colonized community that lives inside the tumor,” which remains a matter of debate, Dr. Vujkovic-Cvijin said.

A 2020 study in Science suggested diverse microbial communities in seven tumor types, but those findings were similarly called into question. That study stated that “bacteria were first detected in human tumors more than 100 years ago” and that “bacteria are well-known residents in human tumors,” but Dr. Salzberg considers those statements misleading. 

It’s true that bacteria and viruses have been detected in tumors because “there’s very good evidence that an acute infection caused by a very small number of viruses and bacteria can cause a tumor,” Dr. Salzberg said. Human papillomavirus, for example, can cause six different types of cancer. Inflammation and ulcers caused by Helicobacter pylori may progress to stomach cancer, and Fusobacterium nucleatum and Enterococcus faecalis have been shown to contribute to colorectal cancer. Those examples differ from a microbiome; this “a community of bacteria and possibly other microscopic bugs, like fungi, that are happily living in the tumor” the same way microbes reside in our guts, he said.

Dr. Knight said that many bacteria his team identified “have been confirmed independently in subsequent work.” He acknowledged, however, that more research is needed. 

Several of the contested studies above were among a lengthy list that Dr. Knight provided, noting that most of the disagreements “have two sides to them, and critiques from one particular group does not immediately invalidate a reported finding.” 

Yet, many of the papers Dr. Knight listed are precisely the types that skeptics like Dr. Salzberg believe are too flawed to draw reliable conclusions. 

“I think many agree that microbes may exist within tumors that are exposed to the environment, like tumors of the skin, gut, and mouth,” Dr. Vujkovic-Cvijin said. It’s less clear, however, whether tumors further from the body’s microbiome harbor any microbes or where they came from if they do. Microbial signals in organs elsewhere in the body become faint quickly, he said.
 

Underdeveloped Technology 

Though Dr. Salzberg said that the concept of a tumor microbiome is “implausible” because there’s no easy route for bacteria to reach internal organs, it’s unclear whether scientists have the technology yet to adequately answer this question. 

For one thing, samples in these types of studies are typically “ultra-low biomass samples, where the signal — the amount of microbes in the sample — is so low that it’s comparable to how much would be expected to be found in reagents and environmental contamination through processing,” Dr. Vujkovic-Cvijin explained. Many polymerases used to amplify a DNA signal, for example, are made in bacteria and may retain trace amounts identified in these studies. 

Dr. Knight agreed that low biomass is a challenge in this field but is not an unsurmountable one. 

Another challenge is that study samples, as with Dr. Knight’s work, were collected during routine surgeries without the intent to find a microbial signal. Simply using a scalpel to cut through the skin means cutting through a layer of bacteria, and surgery rooms are not designed to eliminate all bacteria. Some work has even shown there is a “hospital microbiome,” so “you can easily have that creep into your signal and mistake it for tumor-resident bacteria,” Dr. Vujkovic-Cvijin said. 

Dr. Knight asserted that the samples are taken under sterile conditions, but other researchers do not think the level of sterility necessary for completely clean samples is possible. 

“Just because it’s in your sample doesn’t mean it was in your tumor,” Dr. Gihawi said.

Even if scientists can retrieve a reliable sample without contamination, analyzing it requires comparing the genetic material to existing databases of microbial genomes. Yet, contamination and misclassification of genetic sequences can be problems in those reference genomes too, Dr. Gihawi explained.

Machine learning algorithms have a role in interpreting data, but “we need to be careful of what we use them for,” he added.

“These techniques are in their infancy, and we’re starting to chase them down, which is why we need to move microbiome research in a way that can be used clinically,” Dr. Gihawi said. 
 

Influence on Cancer Treatment Outcomes

Again, however, the question of whether microbiomes exist within tumors is only one slice of the much larger field looking at microbiomes and cancer, including its influence on cancer treatment outcomes. Although much remains to be learned, less controversy exists over the thousands of studies in the past two decades that have gradually revealed how the body’s microbiome can affect both the course of a cancer and the effectiveness of different treatments.

The growing research showing the importance of the gut microbiome in cancer treatments is not surprising given its role in immunity more broadly. Because the human immune system must recognize and defend against microbes, the microbiome helps train it, Dr. Vujkovic-Cvijin said. 

Some bacteria can escape the gut — a phenomenon called bacterial translocation — and may aid in fighting tumors. To grow large enough to be seen on imaging, tumors need to evolve several abilities, such as growing enough vascularization to receive blood flow and shutting down local immune responses.

“Any added boost, like immunotherapy, has a chance of breaking through that immune forcefield and killing the tumor cells,” Dr. Vujkovic-Cvijin said. Escaped gut bacteria may provide that boost. 

“There’s a lot of evidence that depletion of the gut microbiome impairs immunotherapy and chemotherapy. The thinking behind some of those studies is that gut microbes can cross the gut barrier and when they do, they activate the immune system,” he said. 

In mice engineered to have sterile guts, for example, the lack of bacteria results in less effective immune systems, Dr. Vujkovic-Cvijin pointed out. A host of research has shown that antibiotic exposure during and even 6 months before immunotherapy dramatically reduces survival rates. “That’s pretty convincing to me that gut microbes are important,” he said. 

Dr. Vujkovic-Cvijin cautioned that there continues to be controversy on understanding which bacteria are important for response to immunotherapy. “The field is still in its infancy in terms of understanding which bacteria are most important for these effects,” he said.

Dr. Knight suggested that escaped bacteria may be the genesis of the ones that he and other researchers believe exist in tumors. “Because tumor microbes must come from somewhere, it is to be expected that some of those microbes will be co-opted from body-site specific commensals.”

It’s also possible that metabolites released from gut bacteria escape the gut and could theoretically affect distant tumor growth, Dr. Gihawi said. The most promising avenue of research in this area is metabolites being used as biomarkers, added Dr. Gihawi, whose lab published research on a link between bacteria detected in men’s urine and a more aggressive subset of prostate cancers. But that research is not far enough along to develop lab tests for clinical use, he noted. 
 

No Consensus Yet

Even before the controversy erupted around Dr. Knight’s research, he co-founded the company Micronoma to develop cancer tests based on his microbe findings. The company has raised $17.5 million from private investors as of August 2023 and received the US Food and Drug Administration’s Breakthrough Device designation, allowing the firm to fast-track clinical trials testing the technology. The recent critiques have not changed the company’s plans. 

It’s safe to say that scientists will continue to research and debate the possibility of tumor microbiomes until a consensus emerges. 

“The field is evolving and studies testing the reproducibility of tumor-resident microbial signals are essential for developing our understanding in this area,” Dr. Vujkovic-Cvijin said.

Even if that path ultimately leads nowhere, as Dr. Salzberg expects, research into microbiomes and cancer has plenty of other directions to go.

“I’m actually quite an optimist,” Dr. Gihawi said. “I think there’s a lot of scope for some really good research here, especially in the sites where we know there is a strong microbiome, such as the gastrointestinal tract.”

A version of this article appeared on Medscape.com.

A contentious scientific debate is clouding prospects for a deeper understanding of the microbiome’s role in cancer, a relatively young field of research that some believe could lead to breakthroughs in the diagnosis and treatment of the second-leading cause of death in the United States. 

Last year, the controversy heightened when experts questioned a high-profile study — a 2020 analysis claiming that the tumors of 33 different cancers had their own unique microbiomes — on whether the “signature” of these bacterial compositions could help diagnose cancer.

The incident renewed the spotlight on “tumor microbiomes” because of the bold claims of the original paper and the strongly worded refutations of those claims. The broader field has focused primarily on ways the body’s microbiome interacts with cancers and cancer treatment.

This controversy has highlighted the challenges of making headway in a field where researchers may not even have the tools yet to puzzle-out the wide-ranging implications the microbiome holds for cancer diagnosis and treatment.

But it is also part of a provocative question within that larger field: whether tumors in the body, far from the natural microbiome in the gut, have their own thriving communities of bacteria, viruses, and fungi. And, if they do, how do those tumor microbiomes affect the development and progression of the cancer and the effectiveness of cancer therapies? 
 

Cancer Controversy

The evidence is undeniable that some microbes can directly cause certain cancers and that the human gut microbiome can influence the effectiveness of certain therapies. Beyond that established science, however, the research has raised as many questions as answers about what we do and don’t know about microbiota and cancer.

The only confirmed microbiomes are on the skin and in the gut, mouth, and vagina, which are all areas with an easy direct route for bacteria to enter and grow in or on the body. A series of papers in recent years have suggested that other internal organs, and tumors within them, may have their own microbiomes. 

“Whether microbes exist in tumors of internal organs beyond body surfaces exposed to the environment is a different matter,” said Ivan Vujkovic-Cvijin, PhD, an assistant professor of biomedical sciences and gastroenterology at Cedars-Sinai Medical Center in Los Angeles, whose lab studies how human gut microbes affect inflammatory diseases. “We’ve only recently had the tools to study that question on a molecular level, and the reported results have been conflicting.” 

For example, research allegedly identified microbiota in the human placenta nearly one decade ago. But subsequent research contradicted those claims and showed that the source of the “placental microbiome” was actually contamination. Subsequent similar studies for other parts of the body faced the same scrutiny and, often, eventual debunking.

“Most likely, our immune system has undergone selective pressure to eliminate everything that crosses the gut barrier because there’s not much benefit to the body to have bacteria run amok in our internal organs,” Dr. Vujkovic-Cvijin said. “That can only disrupt the functioning of our tissues, to have an external organism living inside them.” 

The controversy that erupted last summer, surrounding research from the lab of Rob Knight, PhD, at the University of California, San Diego, centered on a slightly different but related question: Could tumors harbor their own microbiomes?

This news organization spoke with two of the authors who published a paper contesting Dr. Knight’s findings: Steven Salzberg, PhD, a professor of biomedical engineering at John Hopkins Medicine, Baltimore, Maryland, and Abraham Gihawi, PhD, a research fellow at Norwich Medical School at the University of East Anglia in the United Kingdom. 

Dr. Salzberg described two major problems with Dr. Knight’s study. 

“What they found were false positives because of contamination in the database and flaws in their methods,” Dr. Salzberg said. “I can’t prove there’s no cancer microbiome, but I can say the cancer microbiomes that they reported don’t exist because the species they were finding aren’t there.”

Dr. Knight disagrees with Dr. Salzberg’s findings, noting that Dr. Salzberg and his co-authors did not examine the publicly available databases used in his study. In a written response, he said that his team’s examination of the database revealed that less than 1% of the microbial genomes overlapped with human ones and that removing them did not change their findings.

Dr. Knight also noted that his team could still “distinguish cancer types by their microbiome” even after running their analysis without the technique that Dr. Salzberg found fault with.

Dr. Salzberg said that the database linked above is not the one Dr. Knight’s study used, however. “The primary database in their study was never made public (it’s too large, they said), and it has/had about 69,000 genomes,” Dr. Salzberg said by email. “But even if we did, this is irrelevant. He’s trying to distract from the primary errors in their study,” which Dr. Salzberg said Dr. Knight’s team has not addressed. 

The critiques Dr. Salzberg raised have been leveled at other studies investigating microbiomes specifically within tumors and independent of the body’s microbiome.

For example, a 2019 study in Nature described a fungal microbiome in pancreatic cancer that a Nature paper 4 years later directly contradicted, citing flaws that invalidated the original findings. A different 2019 study in Cell examined pancreatic tumor microbiota and patient outcomes, but it’s unclear whether the microorganisms moved from the gut to the pancreas or “constitute a durably colonized community that lives inside the tumor,” which remains a matter of debate, Dr. Vujkovic-Cvijin said.

A 2020 study in Science suggested diverse microbial communities in seven tumor types, but those findings were similarly called into question. That study stated that “bacteria were first detected in human tumors more than 100 years ago” and that “bacteria are well-known residents in human tumors,” but Dr. Salzberg considers those statements misleading. 

It’s true that bacteria and viruses have been detected in tumors because “there’s very good evidence that an acute infection caused by a very small number of viruses and bacteria can cause a tumor,” Dr. Salzberg said. Human papillomavirus, for example, can cause six different types of cancer. Inflammation and ulcers caused by Helicobacter pylori may progress to stomach cancer, and Fusobacterium nucleatum and Enterococcus faecalis have been shown to contribute to colorectal cancer. Those examples differ from a microbiome; this “a community of bacteria and possibly other microscopic bugs, like fungi, that are happily living in the tumor” the same way microbes reside in our guts, he said.

Dr. Knight said that many bacteria his team identified “have been confirmed independently in subsequent work.” He acknowledged, however, that more research is needed. 

Several of the contested studies above were among a lengthy list that Dr. Knight provided, noting that most of the disagreements “have two sides to them, and critiques from one particular group does not immediately invalidate a reported finding.” 

Yet, many of the papers Dr. Knight listed are precisely the types that skeptics like Dr. Salzberg believe are too flawed to draw reliable conclusions. 

“I think many agree that microbes may exist within tumors that are exposed to the environment, like tumors of the skin, gut, and mouth,” Dr. Vujkovic-Cvijin said. It’s less clear, however, whether tumors further from the body’s microbiome harbor any microbes or where they came from if they do. Microbial signals in organs elsewhere in the body become faint quickly, he said.
 

Underdeveloped Technology 

Though Dr. Salzberg said that the concept of a tumor microbiome is “implausible” because there’s no easy route for bacteria to reach internal organs, it’s unclear whether scientists have the technology yet to adequately answer this question. 

For one thing, samples in these types of studies are typically “ultra-low biomass samples, where the signal — the amount of microbes in the sample — is so low that it’s comparable to how much would be expected to be found in reagents and environmental contamination through processing,” Dr. Vujkovic-Cvijin explained. Many polymerases used to amplify a DNA signal, for example, are made in bacteria and may retain trace amounts identified in these studies. 

Dr. Knight agreed that low biomass is a challenge in this field but is not an unsurmountable one. 

Another challenge is that study samples, as with Dr. Knight’s work, were collected during routine surgeries without the intent to find a microbial signal. Simply using a scalpel to cut through the skin means cutting through a layer of bacteria, and surgery rooms are not designed to eliminate all bacteria. Some work has even shown there is a “hospital microbiome,” so “you can easily have that creep into your signal and mistake it for tumor-resident bacteria,” Dr. Vujkovic-Cvijin said. 

Dr. Knight asserted that the samples are taken under sterile conditions, but other researchers do not think the level of sterility necessary for completely clean samples is possible. 

“Just because it’s in your sample doesn’t mean it was in your tumor,” Dr. Gihawi said.

Even if scientists can retrieve a reliable sample without contamination, analyzing it requires comparing the genetic material to existing databases of microbial genomes. Yet, contamination and misclassification of genetic sequences can be problems in those reference genomes too, Dr. Gihawi explained.

Machine learning algorithms have a role in interpreting data, but “we need to be careful of what we use them for,” he added.

“These techniques are in their infancy, and we’re starting to chase them down, which is why we need to move microbiome research in a way that can be used clinically,” Dr. Gihawi said. 
 

Influence on Cancer Treatment Outcomes

Again, however, the question of whether microbiomes exist within tumors is only one slice of the much larger field looking at microbiomes and cancer, including its influence on cancer treatment outcomes. Although much remains to be learned, less controversy exists over the thousands of studies in the past two decades that have gradually revealed how the body’s microbiome can affect both the course of a cancer and the effectiveness of different treatments.

The growing research showing the importance of the gut microbiome in cancer treatments is not surprising given its role in immunity more broadly. Because the human immune system must recognize and defend against microbes, the microbiome helps train it, Dr. Vujkovic-Cvijin said. 

Some bacteria can escape the gut — a phenomenon called bacterial translocation — and may aid in fighting tumors. To grow large enough to be seen on imaging, tumors need to evolve several abilities, such as growing enough vascularization to receive blood flow and shutting down local immune responses.

“Any added boost, like immunotherapy, has a chance of breaking through that immune forcefield and killing the tumor cells,” Dr. Vujkovic-Cvijin said. Escaped gut bacteria may provide that boost. 

“There’s a lot of evidence that depletion of the gut microbiome impairs immunotherapy and chemotherapy. The thinking behind some of those studies is that gut microbes can cross the gut barrier and when they do, they activate the immune system,” he said. 

In mice engineered to have sterile guts, for example, the lack of bacteria results in less effective immune systems, Dr. Vujkovic-Cvijin pointed out. A host of research has shown that antibiotic exposure during and even 6 months before immunotherapy dramatically reduces survival rates. “That’s pretty convincing to me that gut microbes are important,” he said. 

Dr. Vujkovic-Cvijin cautioned that there continues to be controversy on understanding which bacteria are important for response to immunotherapy. “The field is still in its infancy in terms of understanding which bacteria are most important for these effects,” he said.

Dr. Knight suggested that escaped bacteria may be the genesis of the ones that he and other researchers believe exist in tumors. “Because tumor microbes must come from somewhere, it is to be expected that some of those microbes will be co-opted from body-site specific commensals.”

It’s also possible that metabolites released from gut bacteria escape the gut and could theoretically affect distant tumor growth, Dr. Gihawi said. The most promising avenue of research in this area is metabolites being used as biomarkers, added Dr. Gihawi, whose lab published research on a link between bacteria detected in men’s urine and a more aggressive subset of prostate cancers. But that research is not far enough along to develop lab tests for clinical use, he noted. 
 

No Consensus Yet

Even before the controversy erupted around Dr. Knight’s research, he co-founded the company Micronoma to develop cancer tests based on his microbe findings. The company has raised $17.5 million from private investors as of August 2023 and received the US Food and Drug Administration’s Breakthrough Device designation, allowing the firm to fast-track clinical trials testing the technology. The recent critiques have not changed the company’s plans. 

It’s safe to say that scientists will continue to research and debate the possibility of tumor microbiomes until a consensus emerges. 

“The field is evolving and studies testing the reproducibility of tumor-resident microbial signals are essential for developing our understanding in this area,” Dr. Vujkovic-Cvijin said.

Even if that path ultimately leads nowhere, as Dr. Salzberg expects, research into microbiomes and cancer has plenty of other directions to go.

“I’m actually quite an optimist,” Dr. Gihawi said. “I think there’s a lot of scope for some really good research here, especially in the sites where we know there is a strong microbiome, such as the gastrointestinal tract.”

A version of this article appeared on Medscape.com.

A contentious scientific debate is clouding prospects for a deeper understanding of the microbiome’s role in cancer, a relatively young field of research that some believe could lead to breakthroughs in the diagnosis and treatment of the second-leading cause of death in the United States. 

Last year, the controversy heightened when experts questioned a high-profile study — a 2020 analysis claiming that the tumors of 33 different cancers had their own unique microbiomes — on whether the “signature” of these bacterial compositions could help diagnose cancer.

The incident renewed the spotlight on “tumor microbiomes” because of the bold claims of the original paper and the strongly worded refutations of those claims. The broader field has focused primarily on ways the body’s microbiome interacts with cancers and cancer treatment.

This controversy has highlighted the challenges of making headway in a field where researchers may not even have the tools yet to puzzle-out the wide-ranging implications the microbiome holds for cancer diagnosis and treatment.

But it is also part of a provocative question within that larger field: whether tumors in the body, far from the natural microbiome in the gut, have their own thriving communities of bacteria, viruses, and fungi. And, if they do, how do those tumor microbiomes affect the development and progression of the cancer and the effectiveness of cancer therapies? 
 

Cancer Controversy

The evidence is undeniable that some microbes can directly cause certain cancers and that the human gut microbiome can influence the effectiveness of certain therapies. Beyond that established science, however, the research has raised as many questions as answers about what we do and don’t know about microbiota and cancer.

The only confirmed microbiomes are on the skin and in the gut, mouth, and vagina, which are all areas with an easy direct route for bacteria to enter and grow in or on the body. A series of papers in recent years have suggested that other internal organs, and tumors within them, may have their own microbiomes. 

“Whether microbes exist in tumors of internal organs beyond body surfaces exposed to the environment is a different matter,” said Ivan Vujkovic-Cvijin, PhD, an assistant professor of biomedical sciences and gastroenterology at Cedars-Sinai Medical Center in Los Angeles, whose lab studies how human gut microbes affect inflammatory diseases. “We’ve only recently had the tools to study that question on a molecular level, and the reported results have been conflicting.” 

For example, research allegedly identified microbiota in the human placenta nearly one decade ago. But subsequent research contradicted those claims and showed that the source of the “placental microbiome” was actually contamination. Subsequent similar studies for other parts of the body faced the same scrutiny and, often, eventual debunking.

“Most likely, our immune system has undergone selective pressure to eliminate everything that crosses the gut barrier because there’s not much benefit to the body to have bacteria run amok in our internal organs,” Dr. Vujkovic-Cvijin said. “That can only disrupt the functioning of our tissues, to have an external organism living inside them.” 

The controversy that erupted last summer, surrounding research from the lab of Rob Knight, PhD, at the University of California, San Diego, centered on a slightly different but related question: Could tumors harbor their own microbiomes?

This news organization spoke with two of the authors who published a paper contesting Dr. Knight’s findings: Steven Salzberg, PhD, a professor of biomedical engineering at John Hopkins Medicine, Baltimore, Maryland, and Abraham Gihawi, PhD, a research fellow at Norwich Medical School at the University of East Anglia in the United Kingdom. 

Dr. Salzberg described two major problems with Dr. Knight’s study. 

“What they found were false positives because of contamination in the database and flaws in their methods,” Dr. Salzberg said. “I can’t prove there’s no cancer microbiome, but I can say the cancer microbiomes that they reported don’t exist because the species they were finding aren’t there.”

Dr. Knight disagrees with Dr. Salzberg’s findings, noting that Dr. Salzberg and his co-authors did not examine the publicly available databases used in his study. In a written response, he said that his team’s examination of the database revealed that less than 1% of the microbial genomes overlapped with human ones and that removing them did not change their findings.

Dr. Knight also noted that his team could still “distinguish cancer types by their microbiome” even after running their analysis without the technique that Dr. Salzberg found fault with.

Dr. Salzberg said that the database linked above is not the one Dr. Knight’s study used, however. “The primary database in their study was never made public (it’s too large, they said), and it has/had about 69,000 genomes,” Dr. Salzberg said by email. “But even if we did, this is irrelevant. He’s trying to distract from the primary errors in their study,” which Dr. Salzberg said Dr. Knight’s team has not addressed. 

The critiques Dr. Salzberg raised have been leveled at other studies investigating microbiomes specifically within tumors and independent of the body’s microbiome.

For example, a 2019 study in Nature described a fungal microbiome in pancreatic cancer that a Nature paper 4 years later directly contradicted, citing flaws that invalidated the original findings. A different 2019 study in Cell examined pancreatic tumor microbiota and patient outcomes, but it’s unclear whether the microorganisms moved from the gut to the pancreas or “constitute a durably colonized community that lives inside the tumor,” which remains a matter of debate, Dr. Vujkovic-Cvijin said.

A 2020 study in Science suggested diverse microbial communities in seven tumor types, but those findings were similarly called into question. That study stated that “bacteria were first detected in human tumors more than 100 years ago” and that “bacteria are well-known residents in human tumors,” but Dr. Salzberg considers those statements misleading. 

It’s true that bacteria and viruses have been detected in tumors because “there’s very good evidence that an acute infection caused by a very small number of viruses and bacteria can cause a tumor,” Dr. Salzberg said. Human papillomavirus, for example, can cause six different types of cancer. Inflammation and ulcers caused by Helicobacter pylori may progress to stomach cancer, and Fusobacterium nucleatum and Enterococcus faecalis have been shown to contribute to colorectal cancer. Those examples differ from a microbiome; this “a community of bacteria and possibly other microscopic bugs, like fungi, that are happily living in the tumor” the same way microbes reside in our guts, he said.

Dr. Knight said that many bacteria his team identified “have been confirmed independently in subsequent work.” He acknowledged, however, that more research is needed. 

Several of the contested studies above were among a lengthy list that Dr. Knight provided, noting that most of the disagreements “have two sides to them, and critiques from one particular group does not immediately invalidate a reported finding.” 

Yet, many of the papers Dr. Knight listed are precisely the types that skeptics like Dr. Salzberg believe are too flawed to draw reliable conclusions. 

“I think many agree that microbes may exist within tumors that are exposed to the environment, like tumors of the skin, gut, and mouth,” Dr. Vujkovic-Cvijin said. It’s less clear, however, whether tumors further from the body’s microbiome harbor any microbes or where they came from if they do. Microbial signals in organs elsewhere in the body become faint quickly, he said.
 

Underdeveloped Technology 

Though Dr. Salzberg said that the concept of a tumor microbiome is “implausible” because there’s no easy route for bacteria to reach internal organs, it’s unclear whether scientists have the technology yet to adequately answer this question. 

For one thing, samples in these types of studies are typically “ultra-low biomass samples, where the signal — the amount of microbes in the sample — is so low that it’s comparable to how much would be expected to be found in reagents and environmental contamination through processing,” Dr. Vujkovic-Cvijin explained. Many polymerases used to amplify a DNA signal, for example, are made in bacteria and may retain trace amounts identified in these studies. 

Dr. Knight agreed that low biomass is a challenge in this field but is not an unsurmountable one. 

Another challenge is that study samples, as with Dr. Knight’s work, were collected during routine surgeries without the intent to find a microbial signal. Simply using a scalpel to cut through the skin means cutting through a layer of bacteria, and surgery rooms are not designed to eliminate all bacteria. Some work has even shown there is a “hospital microbiome,” so “you can easily have that creep into your signal and mistake it for tumor-resident bacteria,” Dr. Vujkovic-Cvijin said. 

Dr. Knight asserted that the samples are taken under sterile conditions, but other researchers do not think the level of sterility necessary for completely clean samples is possible. 

“Just because it’s in your sample doesn’t mean it was in your tumor,” Dr. Gihawi said.

Even if scientists can retrieve a reliable sample without contamination, analyzing it requires comparing the genetic material to existing databases of microbial genomes. Yet, contamination and misclassification of genetic sequences can be problems in those reference genomes too, Dr. Gihawi explained.

Machine learning algorithms have a role in interpreting data, but “we need to be careful of what we use them for,” he added.

“These techniques are in their infancy, and we’re starting to chase them down, which is why we need to move microbiome research in a way that can be used clinically,” Dr. Gihawi said. 
 

Influence on Cancer Treatment Outcomes

Again, however, the question of whether microbiomes exist within tumors is only one slice of the much larger field looking at microbiomes and cancer, including its influence on cancer treatment outcomes. Although much remains to be learned, less controversy exists over the thousands of studies in the past two decades that have gradually revealed how the body’s microbiome can affect both the course of a cancer and the effectiveness of different treatments.

The growing research showing the importance of the gut microbiome in cancer treatments is not surprising given its role in immunity more broadly. Because the human immune system must recognize and defend against microbes, the microbiome helps train it, Dr. Vujkovic-Cvijin said. 

Some bacteria can escape the gut — a phenomenon called bacterial translocation — and may aid in fighting tumors. To grow large enough to be seen on imaging, tumors need to evolve several abilities, such as growing enough vascularization to receive blood flow and shutting down local immune responses.

“Any added boost, like immunotherapy, has a chance of breaking through that immune forcefield and killing the tumor cells,” Dr. Vujkovic-Cvijin said. Escaped gut bacteria may provide that boost. 

“There’s a lot of evidence that depletion of the gut microbiome impairs immunotherapy and chemotherapy. The thinking behind some of those studies is that gut microbes can cross the gut barrier and when they do, they activate the immune system,” he said. 

In mice engineered to have sterile guts, for example, the lack of bacteria results in less effective immune systems, Dr. Vujkovic-Cvijin pointed out. A host of research has shown that antibiotic exposure during and even 6 months before immunotherapy dramatically reduces survival rates. “That’s pretty convincing to me that gut microbes are important,” he said. 

Dr. Vujkovic-Cvijin cautioned that there continues to be controversy on understanding which bacteria are important for response to immunotherapy. “The field is still in its infancy in terms of understanding which bacteria are most important for these effects,” he said.

Dr. Knight suggested that escaped bacteria may be the genesis of the ones that he and other researchers believe exist in tumors. “Because tumor microbes must come from somewhere, it is to be expected that some of those microbes will be co-opted from body-site specific commensals.”

It’s also possible that metabolites released from gut bacteria escape the gut and could theoretically affect distant tumor growth, Dr. Gihawi said. The most promising avenue of research in this area is metabolites being used as biomarkers, added Dr. Gihawi, whose lab published research on a link between bacteria detected in men’s urine and a more aggressive subset of prostate cancers. But that research is not far enough along to develop lab tests for clinical use, he noted. 
 

No Consensus Yet

Even before the controversy erupted around Dr. Knight’s research, he co-founded the company Micronoma to develop cancer tests based on his microbe findings. The company has raised $17.5 million from private investors as of August 2023 and received the US Food and Drug Administration’s Breakthrough Device designation, allowing the firm to fast-track clinical trials testing the technology. The recent critiques have not changed the company’s plans. 

It’s safe to say that scientists will continue to research and debate the possibility of tumor microbiomes until a consensus emerges. 

“The field is evolving and studies testing the reproducibility of tumor-resident microbial signals are essential for developing our understanding in this area,” Dr. Vujkovic-Cvijin said.

Even if that path ultimately leads nowhere, as Dr. Salzberg expects, research into microbiomes and cancer has plenty of other directions to go.

“I’m actually quite an optimist,” Dr. Gihawi said. “I think there’s a lot of scope for some really good research here, especially in the sites where we know there is a strong microbiome, such as the gastrointestinal tract.”

A version of this article appeared on Medscape.com.

In the setting of conflicting national screening guidelines, the incidence of distant- and regional-stage colorectal adenocarcinoma (CRC) has been increasing in individuals aged 46-49 years, a cross-sectional study of stage-stratified CRC found.

It is well known that CRC is becoming more prevalent generally in the under 50-year population, but stage-related analyses have not been done.

Staging analysis in this age group is important, however, as an increasing burden of advance-staged disease would provide further evidence for earlier screening initiation, wrote Eric M. Montminy, MD, a gastroenterologist at John H. Stroger Hospital of County Cook, Chicago, Illinois, and colleagues in JAMA Network Open.

• Distant adenocarcinoma IRs increased faster than other stages: annual percentage change (APC), 2.2 (95% CI, 1.8-2.6).
• Regional IRs also significantly increased: APC, 1.3 (95% CI, 0.8-1.7).
• Absolute regional IRs of CRC in the age bracket of 46-49 years are similar to total pancreatic cancer IRs in all ages and all stages combined (13.2 of 100,000) over similar years. When distant IRs for CRC are included with regional IRs, those for IRs for CRC are double those for pancreatic cancer of all stages combined.
• The only decrease was seen in localized IRs: APC, -0.6 (95% CI, -1 to -0.2).

“My best advice for clinicians is to provide the facts from the data to patients so they can make an informed health decision,” Dr. Montminy said. “This includes taking an appropriate personal and family history and having the patient factor this aspect into their decision on when and how they want to perform colon cancer screening.”

His institution adheres to the USPSTF recommendation of initiation of CRC screening at age 45 years.
 

Findings From 2000 to 2020

During 2000-2020 period, 26,887 CRCs were diagnosed in adults aged 46-49 years (54.5% in men).

As of 2020, the localized adenocarcinoma IR decreased to 7.7 of 100,000, but regional adenocarcinoma IR increased to 13.4 of 100,000 and distant adenocarcinoma IR increased to 9.0 of 100,000.

Regional adenocarcinoma IR remained the highest of all stages in 2000-2020. From 2014 to 2020, distant IRs became similar to localized IRs, except in 2017 when distant IRs were significantly higher than localized.
 

Why the CRC Uptick?

“It remains an enigma at this time as to why we’re seeing this shift,” Dr. Montminy said, noting that etiologies from the colonic microbiome to cellphones have been postulated. “To date, no theory has substantially provided causality. But whatever the source is, it is affecting Western countries in unison with data demonstrating a birth cohort effect as well,” he added. “We additionally know, based on the current epidemiologic data, that current screening practices are failing, and a unified discussion must occur in order to prevent young patients from developing advanced colon cancer.”

Offering his perspective on the findings, Joshua Meyer, MD, vice chair of translational research in the Department of Radiation Oncology at Fox Chase Cancer Center in Philadelphia, said the findings reinforce the practice of offering screening to average-risk individuals starting at age 45 years, the threshold at his institution. “There are previously published data demonstrating an increase in advanced stage at the time of screening initiation, and these data support that,” said Dr. Meyer, who was not involved in the present analysis.

More research needs to be done, he continued, not just on optimal age but also on the effect of multiple other factors impacting risk. “These may include family history and genetic risk as well as the role of blood- and stool-based screening assays in an integrated strategy to screen for colorectal cancer.”

There are multiple screening tests, and while colonoscopy, the gold standard, is very safe, it is not completely without risks, Dr. Meyer added. “And the question of the appropriate allocation of limited societal resources continues to be discussed on a broader level and largely explains the difference between the two guidelines.”

This study received no specific funding. Co-author Jordan J. Karlitz, MD, reported personal fees from GRAIL (senior medical director) and an equity position from Gastro Girl/GI On Demand outside f the submitted work. Dr. Meyer disclosed no conflicts of interest relevant to his comments.

In the setting of conflicting national screening guidelines, the incidence of distant- and regional-stage colorectal adenocarcinoma (CRC) has been increasing in individuals aged 46-49 years, a cross-sectional study of stage-stratified CRC found.

It is well known that CRC is becoming more prevalent generally in the under 50-year population, but stage-related analyses have not been done.

Staging analysis in this age group is important, however, as an increasing burden of advance-staged disease would provide further evidence for earlier screening initiation, wrote Eric M. Montminy, MD, a gastroenterologist at John H. Stroger Hospital of County Cook, Chicago, Illinois, and colleagues in JAMA Network Open.

• Distant adenocarcinoma IRs increased faster than other stages: annual percentage change (APC), 2.2 (95% CI, 1.8-2.6).
• Regional IRs also significantly increased: APC, 1.3 (95% CI, 0.8-1.7).
• Absolute regional IRs of CRC in the age bracket of 46-49 years are similar to total pancreatic cancer IRs in all ages and all stages combined (13.2 of 100,000) over similar years. When distant IRs for CRC are included with regional IRs, those for IRs for CRC are double those for pancreatic cancer of all stages combined.
• The only decrease was seen in localized IRs: APC, -0.6 (95% CI, -1 to -0.2).

“My best advice for clinicians is to provide the facts from the data to patients so they can make an informed health decision,” Dr. Montminy said. “This includes taking an appropriate personal and family history and having the patient factor this aspect into their decision on when and how they want to perform colon cancer screening.”

His institution adheres to the USPSTF recommendation of initiation of CRC screening at age 45 years.
 

Findings From 2000 to 2020

During 2000-2020 period, 26,887 CRCs were diagnosed in adults aged 46-49 years (54.5% in men).

As of 2020, the localized adenocarcinoma IR decreased to 7.7 of 100,000, but regional adenocarcinoma IR increased to 13.4 of 100,000 and distant adenocarcinoma IR increased to 9.0 of 100,000.

Regional adenocarcinoma IR remained the highest of all stages in 2000-2020. From 2014 to 2020, distant IRs became similar to localized IRs, except in 2017 when distant IRs were significantly higher than localized.
 

Why the CRC Uptick?

“It remains an enigma at this time as to why we’re seeing this shift,” Dr. Montminy said, noting that etiologies from the colonic microbiome to cellphones have been postulated. “To date, no theory has substantially provided causality. But whatever the source is, it is affecting Western countries in unison with data demonstrating a birth cohort effect as well,” he added. “We additionally know, based on the current epidemiologic data, that current screening practices are failing, and a unified discussion must occur in order to prevent young patients from developing advanced colon cancer.”

Offering his perspective on the findings, Joshua Meyer, MD, vice chair of translational research in the Department of Radiation Oncology at Fox Chase Cancer Center in Philadelphia, said the findings reinforce the practice of offering screening to average-risk individuals starting at age 45 years, the threshold at his institution. “There are previously published data demonstrating an increase in advanced stage at the time of screening initiation, and these data support that,” said Dr. Meyer, who was not involved in the present analysis.

More research needs to be done, he continued, not just on optimal age but also on the effect of multiple other factors impacting risk. “These may include family history and genetic risk as well as the role of blood- and stool-based screening assays in an integrated strategy to screen for colorectal cancer.”

There are multiple screening tests, and while colonoscopy, the gold standard, is very safe, it is not completely without risks, Dr. Meyer added. “And the question of the appropriate allocation of limited societal resources continues to be discussed on a broader level and largely explains the difference between the two guidelines.”

This study received no specific funding. Co-author Jordan J. Karlitz, MD, reported personal fees from GRAIL (senior medical director) and an equity position from Gastro Girl/GI On Demand outside f the submitted work. Dr. Meyer disclosed no conflicts of interest relevant to his comments.

In the setting of conflicting national screening guidelines, the incidence of distant- and regional-stage colorectal adenocarcinoma (CRC) has been increasing in individuals aged 46-49 years, a cross-sectional study of stage-stratified CRC found.

It is well known that CRC is becoming more prevalent generally in the under 50-year population, but stage-related analyses have not been done.

Staging analysis in this age group is important, however, as an increasing burden of advance-staged disease would provide further evidence for earlier screening initiation, wrote Eric M. Montminy, MD, a gastroenterologist at John H. Stroger Hospital of County Cook, Chicago, Illinois, and colleagues in JAMA Network Open.

• Distant adenocarcinoma IRs increased faster than other stages: annual percentage change (APC), 2.2 (95% CI, 1.8-2.6).
• Regional IRs also significantly increased: APC, 1.3 (95% CI, 0.8-1.7).
• Absolute regional IRs of CRC in the age bracket of 46-49 years are similar to total pancreatic cancer IRs in all ages and all stages combined (13.2 of 100,000) over similar years. When distant IRs for CRC are included with regional IRs, those for IRs for CRC are double those for pancreatic cancer of all stages combined.
• The only decrease was seen in localized IRs: APC, -0.6 (95% CI, -1 to -0.2).

“My best advice for clinicians is to provide the facts from the data to patients so they can make an informed health decision,” Dr. Montminy said. “This includes taking an appropriate personal and family history and having the patient factor this aspect into their decision on when and how they want to perform colon cancer screening.”

His institution adheres to the USPSTF recommendation of initiation of CRC screening at age 45 years.
 

Findings From 2000 to 2020

During 2000-2020 period, 26,887 CRCs were diagnosed in adults aged 46-49 years (54.5% in men).

As of 2020, the localized adenocarcinoma IR decreased to 7.7 of 100,000, but regional adenocarcinoma IR increased to 13.4 of 100,000 and distant adenocarcinoma IR increased to 9.0 of 100,000.

Regional adenocarcinoma IR remained the highest of all stages in 2000-2020. From 2014 to 2020, distant IRs became similar to localized IRs, except in 2017 when distant IRs were significantly higher than localized.
 

Why the CRC Uptick?

“It remains an enigma at this time as to why we’re seeing this shift,” Dr. Montminy said, noting that etiologies from the colonic microbiome to cellphones have been postulated. “To date, no theory has substantially provided causality. But whatever the source is, it is affecting Western countries in unison with data demonstrating a birth cohort effect as well,” he added. “We additionally know, based on the current epidemiologic data, that current screening practices are failing, and a unified discussion must occur in order to prevent young patients from developing advanced colon cancer.”

Offering his perspective on the findings, Joshua Meyer, MD, vice chair of translational research in the Department of Radiation Oncology at Fox Chase Cancer Center in Philadelphia, said the findings reinforce the practice of offering screening to average-risk individuals starting at age 45 years, the threshold at his institution. “There are previously published data demonstrating an increase in advanced stage at the time of screening initiation, and these data support that,” said Dr. Meyer, who was not involved in the present analysis.

More research needs to be done, he continued, not just on optimal age but also on the effect of multiple other factors impacting risk. “These may include family history and genetic risk as well as the role of blood- and stool-based screening assays in an integrated strategy to screen for colorectal cancer.”

There are multiple screening tests, and while colonoscopy, the gold standard, is very safe, it is not completely without risks, Dr. Meyer added. “And the question of the appropriate allocation of limited societal resources continues to be discussed on a broader level and largely explains the difference between the two guidelines.”

This study received no specific funding. Co-author Jordan J. Karlitz, MD, reported personal fees from GRAIL (senior medical director) and an equity position from Gastro Girl/GI On Demand outside f the submitted work. Dr. Meyer disclosed no conflicts of interest relevant to his comments.