Yara Abdou, MD

Poly-(ADP-ribose) polymerase (PARP) inhibitors have emerged as essential therapeutic agents in patients with germline BRCA1/2-mutated BC. A BRCA-like phenotype is displayed by a large subset of patients with germline BRCA1/2-wildtype BC who present with homologous recombination deficiency (HRD). The randomized phase 2 S1416 trial (Rodler et al) evaluated the efficacy of cisplatin combined with the PARP inhibitor veliparib in three cohorts of metastatic BC: mutated germline BRCA1/2, BRCA-like, and non-BRCA–like. A total of 335 patients with metastatic or recurrent triple-negative BC (TNBC) or germline BRCA1/2-mutated metastatic BC were randomly assigned (1:1) to receive cisplatin plus either veliparib or a matching placebo. The findings showed that the addition of veliparib to cisplatin significantly improved progression-free survival (PFS) in patients with BRCA-like metastatic TNBC compared with placebo (5.9 vs 4.2 months; HR 0.57; log-rank P = .01), but not in mutated germline BRCA1/2 (6.2 vs 6.4 months; P = .54) and non-BRCA–like (4.0 vs 3.0 months; P = .57) groups. No new toxicity signals were observed. These findings suggest BRCA-like TNBC might show sensitivity to PARP inhibitors and therefore these agents should be explored further in this cohort.

A recent update from the combined analysis of the SOFT and TEXT studies comparing outcomes in 4690 premenopausal women with estrogen/progesterone receptor–positive early BC (Pagani et al) showed that exemestane plus ovarian function suppression (OFS) led to a greater reduction in recurrence risk compared with tamoxifen plus OFS in premenopausal women. After a median follow-up of 13 years, results showed a 4.6% absolute improvement in 12-year disease-free survival (HR 0.79; P < .001) and a 1.8% absolute improvement in disease recurrence-free interval (HR 0.83; P = .03) with exemestane plus OFS compared with tamoxifen plus OFS. These treatment effects on recurrence began to attenuate over time, being strongest in the first 5 years with no further improvement after 10 or more years. No improvement in overall survival (OS) was noted with exemestane vs tamoxifen, although both arms had excellent survival outcomes (90.1% vs 89.1%; HR 0.93; 95% CI 0.78-1.11). It is important to note that there was a 3.3% absolute improvement in 12-year OS with exemestane plus OFS among patients with HER2-negative tumors who received chemotherapy. This OS benefit was also noted amongst patients with high-risk clinicopathologic characteristics (<35 years and those with > 2 cm or grade 3 tumors), ranging from 4.0% to 5.5% absolute improvement. In conclusion, sustained recurrence risk reductions were noted with adjuvant exemestane plus OFS compared with tamoxifen plus OFS, with the most clinically meaningful survival benefit noted for patients with higher risk tumors. Proper selection of patients who are most likely to benefit from exemestane over tamoxifen is vital to maximize the survival benefit while minimizing the burden of treatment intensification.

Findings from a retrospective study including 221 women with BC who received preoperative neoadjuvant chemotherapy (NAC) showed that the presence of metabolic syndrome (MetS) worsened survival outcomes and increased disease recurrence risk (Zhou et al). Patients were divided into MetS and non-MetS groups according to National Cholesterol Education Program Adult Treatment Panel III criteria to investigate the association between MetS and clinicopathologic characteristics, pathologic complete response (pCR), and long-term survival. The MetS group had a significantly lower likelihood of achieving pCR after NAC compared with the non-MetS group (odds ratio [OR] 0.316; P = .028), with the risk for death (OR 2.587; P = .004) and disease recurrence (OR 2.228; P = .007) being significantly higher in patients with vs without MetS. In a multivariate analysis, MetS (P = 0.028) and hormone receptors status were independent predictors of pCR after NAC in BC. These findings emphasize the importance of timely intervention of metabolic syndrome to improve outcomes in patients with BC.

Poly-(ADP-ribose) polymerase (PARP) inhibitors have emerged as essential therapeutic agents in patients with germline BRCA1/2-mutated BC. A BRCA-like phenotype is displayed by a large subset of patients with germline BRCA1/2-wildtype BC who present with homologous recombination deficiency (HRD). The randomized phase 2 S1416 trial (Rodler et al) evaluated the efficacy of cisplatin combined with the PARP inhibitor veliparib in three cohorts of metastatic BC: mutated germline BRCA1/2, BRCA-like, and non-BRCA–like. A total of 335 patients with metastatic or recurrent triple-negative BC (TNBC) or germline BRCA1/2-mutated metastatic BC were randomly assigned (1:1) to receive cisplatin plus either veliparib or a matching placebo. The findings showed that the addition of veliparib to cisplatin significantly improved progression-free survival (PFS) in patients with BRCA-like metastatic TNBC compared with placebo (5.9 vs 4.2 months; HR 0.57; log-rank P = .01), but not in mutated germline BRCA1/2 (6.2 vs 6.4 months; P = .54) and non-BRCA–like (4.0 vs 3.0 months; P = .57) groups. No new toxicity signals were observed. These findings suggest BRCA-like TNBC might show sensitivity to PARP inhibitors and therefore these agents should be explored further in this cohort.

A recent update from the combined analysis of the SOFT and TEXT studies comparing outcomes in 4690 premenopausal women with estrogen/progesterone receptor–positive early BC (Pagani et al) showed that exemestane plus ovarian function suppression (OFS) led to a greater reduction in recurrence risk compared with tamoxifen plus OFS in premenopausal women. After a median follow-up of 13 years, results showed a 4.6% absolute improvement in 12-year disease-free survival (HR 0.79; P < .001) and a 1.8% absolute improvement in disease recurrence-free interval (HR 0.83; P = .03) with exemestane plus OFS compared with tamoxifen plus OFS. These treatment effects on recurrence began to attenuate over time, being strongest in the first 5 years with no further improvement after 10 or more years. No improvement in overall survival (OS) was noted with exemestane vs tamoxifen, although both arms had excellent survival outcomes (90.1% vs 89.1%; HR 0.93; 95% CI 0.78-1.11). It is important to note that there was a 3.3% absolute improvement in 12-year OS with exemestane plus OFS among patients with HER2-negative tumors who received chemotherapy. This OS benefit was also noted amongst patients with high-risk clinicopathologic characteristics (<35 years and those with > 2 cm or grade 3 tumors), ranging from 4.0% to 5.5% absolute improvement. In conclusion, sustained recurrence risk reductions were noted with adjuvant exemestane plus OFS compared with tamoxifen plus OFS, with the most clinically meaningful survival benefit noted for patients with higher risk tumors. Proper selection of patients who are most likely to benefit from exemestane over tamoxifen is vital to maximize the survival benefit while minimizing the burden of treatment intensification.

Findings from a retrospective study including 221 women with BC who received preoperative neoadjuvant chemotherapy (NAC) showed that the presence of metabolic syndrome (MetS) worsened survival outcomes and increased disease recurrence risk (Zhou et al). Patients were divided into MetS and non-MetS groups according to National Cholesterol Education Program Adult Treatment Panel III criteria to investigate the association between MetS and clinicopathologic characteristics, pathologic complete response (pCR), and long-term survival. The MetS group had a significantly lower likelihood of achieving pCR after NAC compared with the non-MetS group (odds ratio [OR] 0.316; P = .028), with the risk for death (OR 2.587; P = .004) and disease recurrence (OR 2.228; P = .007) being significantly higher in patients with vs without MetS. In a multivariate analysis, MetS (P = 0.028) and hormone receptors status were independent predictors of pCR after NAC in BC. These findings emphasize the importance of timely intervention of metabolic syndrome to improve outcomes in patients with BC.

Poly-(ADP-ribose) polymerase (PARP) inhibitors have emerged as essential therapeutic agents in patients with germline BRCA1/2-mutated BC. A BRCA-like phenotype is displayed by a large subset of patients with germline BRCA1/2-wildtype BC who present with homologous recombination deficiency (HRD). The randomized phase 2 S1416 trial (Rodler et al) evaluated the efficacy of cisplatin combined with the PARP inhibitor veliparib in three cohorts of metastatic BC: mutated germline BRCA1/2, BRCA-like, and non-BRCA–like. A total of 335 patients with metastatic or recurrent triple-negative BC (TNBC) or germline BRCA1/2-mutated metastatic BC were randomly assigned (1:1) to receive cisplatin plus either veliparib or a matching placebo. The findings showed that the addition of veliparib to cisplatin significantly improved progression-free survival (PFS) in patients with BRCA-like metastatic TNBC compared with placebo (5.9 vs 4.2 months; HR 0.57; log-rank P = .01), but not in mutated germline BRCA1/2 (6.2 vs 6.4 months; P = .54) and non-BRCA–like (4.0 vs 3.0 months; P = .57) groups. No new toxicity signals were observed. These findings suggest BRCA-like TNBC might show sensitivity to PARP inhibitors and therefore these agents should be explored further in this cohort.

A recent update from the combined analysis of the SOFT and TEXT studies comparing outcomes in 4690 premenopausal women with estrogen/progesterone receptor–positive early BC (Pagani et al) showed that exemestane plus ovarian function suppression (OFS) led to a greater reduction in recurrence risk compared with tamoxifen plus OFS in premenopausal women. After a median follow-up of 13 years, results showed a 4.6% absolute improvement in 12-year disease-free survival (HR 0.79; P < .001) and a 1.8% absolute improvement in disease recurrence-free interval (HR 0.83; P = .03) with exemestane plus OFS compared with tamoxifen plus OFS. These treatment effects on recurrence began to attenuate over time, being strongest in the first 5 years with no further improvement after 10 or more years. No improvement in overall survival (OS) was noted with exemestane vs tamoxifen, although both arms had excellent survival outcomes (90.1% vs 89.1%; HR 0.93; 95% CI 0.78-1.11). It is important to note that there was a 3.3% absolute improvement in 12-year OS with exemestane plus OFS among patients with HER2-negative tumors who received chemotherapy. This OS benefit was also noted amongst patients with high-risk clinicopathologic characteristics (<35 years and those with > 2 cm or grade 3 tumors), ranging from 4.0% to 5.5% absolute improvement. In conclusion, sustained recurrence risk reductions were noted with adjuvant exemestane plus OFS compared with tamoxifen plus OFS, with the most clinically meaningful survival benefit noted for patients with higher risk tumors. Proper selection of patients who are most likely to benefit from exemestane over tamoxifen is vital to maximize the survival benefit while minimizing the burden of treatment intensification.

Findings from a retrospective study including 221 women with BC who received preoperative neoadjuvant chemotherapy (NAC) showed that the presence of metabolic syndrome (MetS) worsened survival outcomes and increased disease recurrence risk (Zhou et al). Patients were divided into MetS and non-MetS groups according to National Cholesterol Education Program Adult Treatment Panel III criteria to investigate the association between MetS and clinicopathologic characteristics, pathologic complete response (pCR), and long-term survival. The MetS group had a significantly lower likelihood of achieving pCR after NAC compared with the non-MetS group (odds ratio [OR] 0.316; P = .028), with the risk for death (OR 2.587; P = .004) and disease recurrence (OR 2.228; P = .007) being significantly higher in patients with vs without MetS. In a multivariate analysis, MetS (P = 0.028) and hormone receptors status were independent predictors of pCR after NAC in BC. These findings emphasize the importance of timely intervention of metabolic syndrome to improve outcomes in patients with BC.

This is the longest reported median PFS in HER2+ metastatic BC, highlighting the potential of trastuzumab deruxtecan in treating this disease and confirming this drug as the standard of care in the second-line setting.

A cohort study evaluated 315 postmenopausal BC survivors to estimate the association of physical activity with risk for all-cause mortality. Participants were queried about leisure-time physical activity using the Godin-Shephard Leisure-Time Physical Activity Questionnaire (GSLTPAQ), which provided a composite score that categorized exercise patterns as active, moderately active, or insufficiently active at baseline.

Results showed that participants who were active or moderately active had a 60% decreased risk for death compared with insufficiently active participants (active: HR 0.42 [95% CI 0.21-0.85]; moderately active: HR 0.40 [95% CI 0.17-0.95]). A similar mortality risk was reported among participants who were active and those with moderate physical activity levels.

Prior studies¹ have reported similar results, reaffirming the value of exercise in BC survivors and highlighting the need to incorporate physical activity as part of survivorship care plans.

The phase 3 SOPHIA study randomized 536 patients with HER2+ advanced BC who had received two or more prior anti-HER2 regimens to margetuximab plus chemotherapy vs trastuzumab plus chemotherapy. Final OS results after a median follow-up of 20.2 months showed no benefit in OS observed with margetuximab vs trastuzumab (median OS 21.6 months vs 21.9 months; HR 0.95; P = .620). The safety profile of margetuximab was acceptable and comparable to that of trastuzumab. Exploratory analysis of CD16A genotyping suggested a possible improvement in OS for margetuximab in CD16A-158FF patients vs trastuzumab (median OS 23.6 vs 19.2 months; HR 0.72; 95% CI 0.52-1.00) and a possible improvement in OS for trastuzumab in CD16A-158VV patients vs margetuximab (median OS 31.1 vs 22.0 months; HR 1.77; 95% CI 1.01–3.12). The safety profile of margetuximab was acceptable and comparable to that of trastuzumab. Further studies to evaluate the role of margetuximab in patients with HER2+ BC with different CD16A allelic variants are warranted.

Additional References

Cannioto RA, Hutson A, Dighe S, et al. Physical activity before, during, and after chemotherapy for high-risk breast cancer: Relationships with survival.  J Natl Cancer Inst. 2021;113:54-63. Doi:10.1093/jnci/djaa046

This is the longest reported median PFS in HER2+ metastatic BC, highlighting the potential of trastuzumab deruxtecan in treating this disease and confirming this drug as the standard of care in the second-line setting.

A cohort study evaluated 315 postmenopausal BC survivors to estimate the association of physical activity with risk for all-cause mortality. Participants were queried about leisure-time physical activity using the Godin-Shephard Leisure-Time Physical Activity Questionnaire (GSLTPAQ), which provided a composite score that categorized exercise patterns as active, moderately active, or insufficiently active at baseline.

Results showed that participants who were active or moderately active had a 60% decreased risk for death compared with insufficiently active participants (active: HR 0.42 [95% CI 0.21-0.85]; moderately active: HR 0.40 [95% CI 0.17-0.95]). A similar mortality risk was reported among participants who were active and those with moderate physical activity levels.

Prior studies¹ have reported similar results, reaffirming the value of exercise in BC survivors and highlighting the need to incorporate physical activity as part of survivorship care plans.

The phase 3 SOPHIA study randomized 536 patients with HER2+ advanced BC who had received two or more prior anti-HER2 regimens to margetuximab plus chemotherapy vs trastuzumab plus chemotherapy. Final OS results after a median follow-up of 20.2 months showed no benefit in OS observed with margetuximab vs trastuzumab (median OS 21.6 months vs 21.9 months; HR 0.95; P = .620). The safety profile of margetuximab was acceptable and comparable to that of trastuzumab. Exploratory analysis of CD16A genotyping suggested a possible improvement in OS for margetuximab in CD16A-158FF patients vs trastuzumab (median OS 23.6 vs 19.2 months; HR 0.72; 95% CI 0.52-1.00) and a possible improvement in OS for trastuzumab in CD16A-158VV patients vs margetuximab (median OS 31.1 vs 22.0 months; HR 1.77; 95% CI 1.01–3.12). The safety profile of margetuximab was acceptable and comparable to that of trastuzumab. Further studies to evaluate the role of margetuximab in patients with HER2+ BC with different CD16A allelic variants are warranted.

Additional References

Cannioto RA, Hutson A, Dighe S, et al. Physical activity before, during, and after chemotherapy for high-risk breast cancer: Relationships with survival.  J Natl Cancer Inst. 2021;113:54-63. Doi:10.1093/jnci/djaa046

This is the longest reported median PFS in HER2+ metastatic BC, highlighting the potential of trastuzumab deruxtecan in treating this disease and confirming this drug as the standard of care in the second-line setting.

A cohort study evaluated 315 postmenopausal BC survivors to estimate the association of physical activity with risk for all-cause mortality. Participants were queried about leisure-time physical activity using the Godin-Shephard Leisure-Time Physical Activity Questionnaire (GSLTPAQ), which provided a composite score that categorized exercise patterns as active, moderately active, or insufficiently active at baseline.

Results showed that participants who were active or moderately active had a 60% decreased risk for death compared with insufficiently active participants (active: HR 0.42 [95% CI 0.21-0.85]; moderately active: HR 0.40 [95% CI 0.17-0.95]). A similar mortality risk was reported among participants who were active and those with moderate physical activity levels.

Prior studies¹ have reported similar results, reaffirming the value of exercise in BC survivors and highlighting the need to incorporate physical activity as part of survivorship care plans.

The phase 3 SOPHIA study randomized 536 patients with HER2+ advanced BC who had received two or more prior anti-HER2 regimens to margetuximab plus chemotherapy vs trastuzumab plus chemotherapy. Final OS results after a median follow-up of 20.2 months showed no benefit in OS observed with margetuximab vs trastuzumab (median OS 21.6 months vs 21.9 months; HR 0.95; P = .620). The safety profile of margetuximab was acceptable and comparable to that of trastuzumab. Exploratory analysis of CD16A genotyping suggested a possible improvement in OS for margetuximab in CD16A-158FF patients vs trastuzumab (median OS 23.6 vs 19.2 months; HR 0.72; 95% CI 0.52-1.00) and a possible improvement in OS for trastuzumab in CD16A-158VV patients vs margetuximab (median OS 31.1 vs 22.0 months; HR 1.77; 95% CI 1.01–3.12). The safety profile of margetuximab was acceptable and comparable to that of trastuzumab. Further studies to evaluate the role of margetuximab in patients with HER2+ BC with different CD16A allelic variants are warranted.

Additional References

Cannioto RA, Hutson A, Dighe S, et al. Physical activity before, during, and after chemotherapy for high-risk breast cancer: Relationships with survival.  J Natl Cancer Inst. 2021;113:54-63. Doi:10.1093/jnci/djaa046

Can you talk about the evolution and treatment of human epidermal growth factor receptor 2 (HER2)-low breast cancer?

Dr. Abdou: Until recently, HER2 status had been defined as a positive or negative result, but this convention has evolved, and now a newly defined population with low levels of HER2 expression has been identified. This HER2-low population accounts for about 55% of all breast cancers. Previously, low HER2 expression levels were considered HER2-negative in clinical practice because HER2-targeted therapies had been considered ineffective in this setting. Patients with HER2-low disease therefore had limited targeted treatment options after progression on their primary therapy.

Now, new studies and clinical trials have opened the door to effective treatments for this cohort of patients. The clinical trial DESTINY-Breast04, which was presented at ASCO 2022, led to the first FDA approval in August 2022 of a targeted therapy option for patients with HER2-low breast cancer subtypes, reclassifying this cohort as a new targetable subset in breast cancer.

DESTINY-Breast04 was the first randomized clinical trial to show that targeting HER2 provides clinically meaningful benefits for patients with HER2-low metastatic breast cancer, not only patients with HER2-positive disease. The phase 3 study enrolled about 557 patients with hormone receptor (HR)-negative or -positive breast cancer and centrally confirmed HER2-low expression who were previously treated with 1 or 2 prior lines of chemotherapy. Patients were randomized to receive either the antibody–drug conjugate trastuzumab deruxtecan or physician’s choice of standard chemotherapy. The risk of disease progression was about 50% lower and the risk of death was about 36% lower with trastuzumab deruxtecan compared with chemotherapy.¹

These impressive and practice-changing results opened the door to a new treatment option for a substantial group of patients with HER2-low disease and significantly expanded the population of patients who can benefit from HER2-targeted therapy.

What molecular characteristics do you take into consideration to help determine whether patients are eligible for these targeted treatment options?

Dr. Abdou: As we said earlier, HER2 status should no longer be recorded as a binary result of either HER2-positive or HER2-negative. It is important to start routinely testing for the level of HER2 expression in the tumor. Obtaining these levels is done through commonly used immunohistochemical (IHC) assays that allow direct visualization of the HER2 protein. Breast tumors considered to be HER2-low are classified as IHC1+ or as IHC2+ with in situ hybridization or FISH-negative status.

HER2-low breast cancer consists of a heterogeneous group of breast cancers, most of which are HR-positive tumors, whereas about 20% are HR-negative tumors. While these tumors may have distinct molecular profiles leading to clinicopathological and prognostic differences within these groups—HR-positive tumors represent more luminal subtypes and HR-negative tumors tend to be predominantly basal-like subtypes—these distinctions do not necessarily affect patient eligibility for targeted therapy. The benefit of trastuzumab deruxtecan was seen in both subgroups, although the HR-positive population was much more well represented in the DESTINY-Breast04 study.

Other than the HER2 expression status, I also take into consideration the presence of clinical comorbidities, particularly pulmonary comorbidities or prior lung injuries. Trastuzumab deruxtecan can cause a potentially serious type of lung toxicity called interstitial lung disease (ILD). In DESTINY-Breast04, ILD developed in about 12% of patients in the trastuzumab deruxtecan group, with 3 deaths as a result.

Therefore, it’s important for us to carefully select these patients and closely monitor them while they’re on treatment.

What is next in the treatment of HER2-low breast cancer, and what would you like to see in the future?

Dr. Abdou: The exciting new field of HER2-low breast cancer has really opened the door to novel studies and clinical trials, several of which are exploring the role of antibody–drug conjugates in patients with metastatic HER2-low disease and others that are studying early-stage HER2-low breast cancer. In early-stage HER2-low breast cancer, we may potentially see an even greater benefit with these drugs because the disease has not yet developed resistance to therapy. Other studies are examining the role of combination therapy in metastatic breast cancer, such as antibody–drug conjugates in combination with immunotherapy and other targeted agents. I look forward to results from those studies.

Also, importantly, as we start using these therapies more widely, I would like to see more accurate and sensitive ways of assessing the HER2 expression status. The current IHC assay, although widely available, fails to identify many women who have HER2 expression in their tumors. I think more sensitive tests may be able to identify even more women who can benefit from these targeted therapies.

Can you talk about the evolution and treatment of human epidermal growth factor receptor 2 (HER2)-low breast cancer?

Dr. Abdou: Until recently, HER2 status had been defined as a positive or negative result, but this convention has evolved, and now a newly defined population with low levels of HER2 expression has been identified. This HER2-low population accounts for about 55% of all breast cancers. Previously, low HER2 expression levels were considered HER2-negative in clinical practice because HER2-targeted therapies had been considered ineffective in this setting. Patients with HER2-low disease therefore had limited targeted treatment options after progression on their primary therapy.

Now, new studies and clinical trials have opened the door to effective treatments for this cohort of patients. The clinical trial DESTINY-Breast04, which was presented at ASCO 2022, led to the first FDA approval in August 2022 of a targeted therapy option for patients with HER2-low breast cancer subtypes, reclassifying this cohort as a new targetable subset in breast cancer.

DESTINY-Breast04 was the first randomized clinical trial to show that targeting HER2 provides clinically meaningful benefits for patients with HER2-low metastatic breast cancer, not only patients with HER2-positive disease. The phase 3 study enrolled about 557 patients with hormone receptor (HR)-negative or -positive breast cancer and centrally confirmed HER2-low expression who were previously treated with 1 or 2 prior lines of chemotherapy. Patients were randomized to receive either the antibody–drug conjugate trastuzumab deruxtecan or physician’s choice of standard chemotherapy. The risk of disease progression was about 50% lower and the risk of death was about 36% lower with trastuzumab deruxtecan compared with chemotherapy.¹

These impressive and practice-changing results opened the door to a new treatment option for a substantial group of patients with HER2-low disease and significantly expanded the population of patients who can benefit from HER2-targeted therapy.

What molecular characteristics do you take into consideration to help determine whether patients are eligible for these targeted treatment options?

Dr. Abdou: As we said earlier, HER2 status should no longer be recorded as a binary result of either HER2-positive or HER2-negative. It is important to start routinely testing for the level of HER2 expression in the tumor. Obtaining these levels is done through commonly used immunohistochemical (IHC) assays that allow direct visualization of the HER2 protein. Breast tumors considered to be HER2-low are classified as IHC1+ or as IHC2+ with in situ hybridization or FISH-negative status.

HER2-low breast cancer consists of a heterogeneous group of breast cancers, most of which are HR-positive tumors, whereas about 20% are HR-negative tumors. While these tumors may have distinct molecular profiles leading to clinicopathological and prognostic differences within these groups—HR-positive tumors represent more luminal subtypes and HR-negative tumors tend to be predominantly basal-like subtypes—these distinctions do not necessarily affect patient eligibility for targeted therapy. The benefit of trastuzumab deruxtecan was seen in both subgroups, although the HR-positive population was much more well represented in the DESTINY-Breast04 study.

Other than the HER2 expression status, I also take into consideration the presence of clinical comorbidities, particularly pulmonary comorbidities or prior lung injuries. Trastuzumab deruxtecan can cause a potentially serious type of lung toxicity called interstitial lung disease (ILD). In DESTINY-Breast04, ILD developed in about 12% of patients in the trastuzumab deruxtecan group, with 3 deaths as a result.

Therefore, it’s important for us to carefully select these patients and closely monitor them while they’re on treatment.

What is next in the treatment of HER2-low breast cancer, and what would you like to see in the future?

Dr. Abdou: The exciting new field of HER2-low breast cancer has really opened the door to novel studies and clinical trials, several of which are exploring the role of antibody–drug conjugates in patients with metastatic HER2-low disease and others that are studying early-stage HER2-low breast cancer. In early-stage HER2-low breast cancer, we may potentially see an even greater benefit with these drugs because the disease has not yet developed resistance to therapy. Other studies are examining the role of combination therapy in metastatic breast cancer, such as antibody–drug conjugates in combination with immunotherapy and other targeted agents. I look forward to results from those studies.

Also, importantly, as we start using these therapies more widely, I would like to see more accurate and sensitive ways of assessing the HER2 expression status. The current IHC assay, although widely available, fails to identify many women who have HER2 expression in their tumors. I think more sensitive tests may be able to identify even more women who can benefit from these targeted therapies.

Can you talk about the evolution and treatment of human epidermal growth factor receptor 2 (HER2)-low breast cancer?

Dr. Abdou: Until recently, HER2 status had been defined as a positive or negative result, but this convention has evolved, and now a newly defined population with low levels of HER2 expression has been identified. This HER2-low population accounts for about 55% of all breast cancers. Previously, low HER2 expression levels were considered HER2-negative in clinical practice because HER2-targeted therapies had been considered ineffective in this setting. Patients with HER2-low disease therefore had limited targeted treatment options after progression on their primary therapy.

Now, new studies and clinical trials have opened the door to effective treatments for this cohort of patients. The clinical trial DESTINY-Breast04, which was presented at ASCO 2022, led to the first FDA approval in August 2022 of a targeted therapy option for patients with HER2-low breast cancer subtypes, reclassifying this cohort as a new targetable subset in breast cancer.

DESTINY-Breast04 was the first randomized clinical trial to show that targeting HER2 provides clinically meaningful benefits for patients with HER2-low metastatic breast cancer, not only patients with HER2-positive disease. The phase 3 study enrolled about 557 patients with hormone receptor (HR)-negative or -positive breast cancer and centrally confirmed HER2-low expression who were previously treated with 1 or 2 prior lines of chemotherapy. Patients were randomized to receive either the antibody–drug conjugate trastuzumab deruxtecan or physician’s choice of standard chemotherapy. The risk of disease progression was about 50% lower and the risk of death was about 36% lower with trastuzumab deruxtecan compared with chemotherapy.¹

These impressive and practice-changing results opened the door to a new treatment option for a substantial group of patients with HER2-low disease and significantly expanded the population of patients who can benefit from HER2-targeted therapy.

What molecular characteristics do you take into consideration to help determine whether patients are eligible for these targeted treatment options?

Dr. Abdou: As we said earlier, HER2 status should no longer be recorded as a binary result of either HER2-positive or HER2-negative. It is important to start routinely testing for the level of HER2 expression in the tumor. Obtaining these levels is done through commonly used immunohistochemical (IHC) assays that allow direct visualization of the HER2 protein. Breast tumors considered to be HER2-low are classified as IHC1+ or as IHC2+ with in situ hybridization or FISH-negative status.

HER2-low breast cancer consists of a heterogeneous group of breast cancers, most of which are HR-positive tumors, whereas about 20% are HR-negative tumors. While these tumors may have distinct molecular profiles leading to clinicopathological and prognostic differences within these groups—HR-positive tumors represent more luminal subtypes and HR-negative tumors tend to be predominantly basal-like subtypes—these distinctions do not necessarily affect patient eligibility for targeted therapy. The benefit of trastuzumab deruxtecan was seen in both subgroups, although the HR-positive population was much more well represented in the DESTINY-Breast04 study.

Other than the HER2 expression status, I also take into consideration the presence of clinical comorbidities, particularly pulmonary comorbidities or prior lung injuries. Trastuzumab deruxtecan can cause a potentially serious type of lung toxicity called interstitial lung disease (ILD). In DESTINY-Breast04, ILD developed in about 12% of patients in the trastuzumab deruxtecan group, with 3 deaths as a result.

Therefore, it’s important for us to carefully select these patients and closely monitor them while they’re on treatment.

What is next in the treatment of HER2-low breast cancer, and what would you like to see in the future?

Dr. Abdou: The exciting new field of HER2-low breast cancer has really opened the door to novel studies and clinical trials, several of which are exploring the role of antibody–drug conjugates in patients with metastatic HER2-low disease and others that are studying early-stage HER2-low breast cancer. In early-stage HER2-low breast cancer, we may potentially see an even greater benefit with these drugs because the disease has not yet developed resistance to therapy. Other studies are examining the role of combination therapy in metastatic breast cancer, such as antibody–drug conjugates in combination with immunotherapy and other targeted agents. I look forward to results from those studies.

Also, importantly, as we start using these therapies more widely, I would like to see more accurate and sensitive ways of assessing the HER2 expression status. The current IHC assay, although widely available, fails to identify many women who have HER2 expression in their tumors. I think more sensitive tests may be able to identify even more women who can benefit from these targeted therapies.

In the PD-L1 CPS ≥ 1 subgroup, however, no significant OS benefit was observed (median OS 17.6 months vs 16.0 months; HR 0.86; 95% CI 0.72-1.04; P = .1125). Additionally, in an exploratory analysis, the addition of pembrolizumab showed consistent OS benefit among patients whose tumors express PD-L1 with a CPS of 10-19 and CPS ≥ 20. The updated progression-free survival (PFS) and objective response rates (ORR) were consistent with prior interim data. No new safety signals were observed after the longer follow-up.

These data confirm that pembrolizumab plus chemotherapy should remain the first-line treatment for patients with advanced or metastatic TNBC whose tumors express PD-L1 with a CPS of ≥ 10. The treatment of metastatic TNBC with low or negative PD-L1 CPS scores remains an area of unmet clinical need, and further research is needed to explore better options for these patients.

Wang and colleagues presented results from a randomized, phase 3 trial comparing first-line nab-paclitaxel plus cisplatin (AP) with gemcitabine plus cisplatin (GP) among 254 patients with previously untreated metastatic TNBC. Median PFS (mPFS) was 9.8 months with AP vs 7.4 months with GP (HR 0.67; 95% CI 0.50-0.88; P  =  .004). Furthermore, AP had significantly higher ORR compared with GP (81.1% vs 56.3%; P  <  .001) and significantly improved median OS (26.3 months vs 22.9 months; HR 0.62; 95% CI 0.44-0.90; P  =  .010).

In the exploratory analyses of PFS by stratification factors, the mPFS was significantly longer in the AP group compared with the GP group in the majority of subgroups, except for those patients who presented with de novo stage IV disease or a disease-free interval of < 1 year. Regarding safety data, a significantly higher incidence of grade ≥ 3 neuropathy (19% vs 0%) and nausea and vomiting (6% vs 1%) was noted in the AP group compared with the GP group, while grade ≥ 3 thrombocytopenia was more common in the GP group compared with the AP group (29.4% vs 3.9%).

The AP doublet achieved superior efficacy with a manageable safety profile, compared with GP in patients with previously untreated metastatic TNBC. It is not clear, however, whether the AP doublet is superior to single-agent therapy in this setting, especially given several prior studies that showed no survival benefit and increased toxicity from combination therapy compared with sequential single-agent therapy in metastatic breast cancer. More studies are needed to establish the role of the AP doublet in combination with pembrolizumab in this cohort of patients, given that first-line pembrolizumab plus chemotherapy is considered the standard of care for patients with metastatic TNBC whose tumors express PD-L1.

Rugo and colleagues presented results from a randomized phase 3 study comparing 205 mg/m²oral paclitaxel plus 15 mg encequidar (a novel P-glycoprotein pump inhibitor that allows oral absorption of paclitaxel) on 3 consecutive days per week vs 175 mg/m² intravenous paclitaxel once every 3 weeks. The study enrolled 402 postmenopausal women from Latin America with metastatic breast cancer who were at least 1 year from their last taxane therapy. Oral paclitaxel plus encequidar (oPac + E) increased the confirmed tumor response compared with intravenous paclitaxel (IVpac) (36% vs 23%; P = .01). There was a trend toward improved PFS (8.4 vs 7.4 months; HR 0.768; 95.5% CI 0.584-1.01; P = .046) and OS (22.7 vs 16.5 months; HR 0.794; 95.5% CI 0.607-1.037; P = .08) with oPac + E compared to IVpac, respectively. Grade ≥3 adverse events were comparable with oPac + E and IVpac (55% vs 53%), although a lower incidence of grade 3 neuropathy (2% vs 15%) and alopecia (49% vs 62%) was noted with oPac + E compared with IVpac. A higher incidence of grade ≥ 3 gastrointestinal toxicity (nausea, vomiting, and diarrhea) and grade 4 neutropenic complications was noted in the oPac + E group. Patients with elevated baseline liver enzymes were particularly susceptible to early neutropenia and serious infections.

This study demonstrates that oral paclitaxel can be a possible alternative treatment option to intravenous paclitaxel in a select group of patients with metastatic breast cancer. High-grade neutropenia appears to be a major treatment-limiting toxicity with oPac + E. Therefore, careful patient selection and close monitoring are crucial for the successful management of this adverse event.

In the PD-L1 CPS ≥ 1 subgroup, however, no significant OS benefit was observed (median OS 17.6 months vs 16.0 months; HR 0.86; 95% CI 0.72-1.04; P = .1125). Additionally, in an exploratory analysis, the addition of pembrolizumab showed consistent OS benefit among patients whose tumors express PD-L1 with a CPS of 10-19 and CPS ≥ 20. The updated progression-free survival (PFS) and objective response rates (ORR) were consistent with prior interim data. No new safety signals were observed after the longer follow-up.

These data confirm that pembrolizumab plus chemotherapy should remain the first-line treatment for patients with advanced or metastatic TNBC whose tumors express PD-L1 with a CPS of ≥ 10. The treatment of metastatic TNBC with low or negative PD-L1 CPS scores remains an area of unmet clinical need, and further research is needed to explore better options for these patients.

Wang and colleagues presented results from a randomized, phase 3 trial comparing first-line nab-paclitaxel plus cisplatin (AP) with gemcitabine plus cisplatin (GP) among 254 patients with previously untreated metastatic TNBC. Median PFS (mPFS) was 9.8 months with AP vs 7.4 months with GP (HR 0.67; 95% CI 0.50-0.88; P  =  .004). Furthermore, AP had significantly higher ORR compared with GP (81.1% vs 56.3%; P  <  .001) and significantly improved median OS (26.3 months vs 22.9 months; HR 0.62; 95% CI 0.44-0.90; P  =  .010).

In the exploratory analyses of PFS by stratification factors, the mPFS was significantly longer in the AP group compared with the GP group in the majority of subgroups, except for those patients who presented with de novo stage IV disease or a disease-free interval of < 1 year. Regarding safety data, a significantly higher incidence of grade ≥ 3 neuropathy (19% vs 0%) and nausea and vomiting (6% vs 1%) was noted in the AP group compared with the GP group, while grade ≥ 3 thrombocytopenia was more common in the GP group compared with the AP group (29.4% vs 3.9%).

The AP doublet achieved superior efficacy with a manageable safety profile, compared with GP in patients with previously untreated metastatic TNBC. It is not clear, however, whether the AP doublet is superior to single-agent therapy in this setting, especially given several prior studies that showed no survival benefit and increased toxicity from combination therapy compared with sequential single-agent therapy in metastatic breast cancer. More studies are needed to establish the role of the AP doublet in combination with pembrolizumab in this cohort of patients, given that first-line pembrolizumab plus chemotherapy is considered the standard of care for patients with metastatic TNBC whose tumors express PD-L1.

Rugo and colleagues presented results from a randomized phase 3 study comparing 205 mg/m²oral paclitaxel plus 15 mg encequidar (a novel P-glycoprotein pump inhibitor that allows oral absorption of paclitaxel) on 3 consecutive days per week vs 175 mg/m² intravenous paclitaxel once every 3 weeks. The study enrolled 402 postmenopausal women from Latin America with metastatic breast cancer who were at least 1 year from their last taxane therapy. Oral paclitaxel plus encequidar (oPac + E) increased the confirmed tumor response compared with intravenous paclitaxel (IVpac) (36% vs 23%; P = .01). There was a trend toward improved PFS (8.4 vs 7.4 months; HR 0.768; 95.5% CI 0.584-1.01; P = .046) and OS (22.7 vs 16.5 months; HR 0.794; 95.5% CI 0.607-1.037; P = .08) with oPac + E compared to IVpac, respectively. Grade ≥3 adverse events were comparable with oPac + E and IVpac (55% vs 53%), although a lower incidence of grade 3 neuropathy (2% vs 15%) and alopecia (49% vs 62%) was noted with oPac + E compared with IVpac. A higher incidence of grade ≥ 3 gastrointestinal toxicity (nausea, vomiting, and diarrhea) and grade 4 neutropenic complications was noted in the oPac + E group. Patients with elevated baseline liver enzymes were particularly susceptible to early neutropenia and serious infections.

This study demonstrates that oral paclitaxel can be a possible alternative treatment option to intravenous paclitaxel in a select group of patients with metastatic breast cancer. High-grade neutropenia appears to be a major treatment-limiting toxicity with oPac + E. Therefore, careful patient selection and close monitoring are crucial for the successful management of this adverse event.

In the PD-L1 CPS ≥ 1 subgroup, however, no significant OS benefit was observed (median OS 17.6 months vs 16.0 months; HR 0.86; 95% CI 0.72-1.04; P = .1125). Additionally, in an exploratory analysis, the addition of pembrolizumab showed consistent OS benefit among patients whose tumors express PD-L1 with a CPS of 10-19 and CPS ≥ 20. The updated progression-free survival (PFS) and objective response rates (ORR) were consistent with prior interim data. No new safety signals were observed after the longer follow-up.

These data confirm that pembrolizumab plus chemotherapy should remain the first-line treatment for patients with advanced or metastatic TNBC whose tumors express PD-L1 with a CPS of ≥ 10. The treatment of metastatic TNBC with low or negative PD-L1 CPS scores remains an area of unmet clinical need, and further research is needed to explore better options for these patients.

Wang and colleagues presented results from a randomized, phase 3 trial comparing first-line nab-paclitaxel plus cisplatin (AP) with gemcitabine plus cisplatin (GP) among 254 patients with previously untreated metastatic TNBC. Median PFS (mPFS) was 9.8 months with AP vs 7.4 months with GP (HR 0.67; 95% CI 0.50-0.88; P  =  .004). Furthermore, AP had significantly higher ORR compared with GP (81.1% vs 56.3%; P  <  .001) and significantly improved median OS (26.3 months vs 22.9 months; HR 0.62; 95% CI 0.44-0.90; P  =  .010).

In the exploratory analyses of PFS by stratification factors, the mPFS was significantly longer in the AP group compared with the GP group in the majority of subgroups, except for those patients who presented with de novo stage IV disease or a disease-free interval of < 1 year. Regarding safety data, a significantly higher incidence of grade ≥ 3 neuropathy (19% vs 0%) and nausea and vomiting (6% vs 1%) was noted in the AP group compared with the GP group, while grade ≥ 3 thrombocytopenia was more common in the GP group compared with the AP group (29.4% vs 3.9%).

The AP doublet achieved superior efficacy with a manageable safety profile, compared with GP in patients with previously untreated metastatic TNBC. It is not clear, however, whether the AP doublet is superior to single-agent therapy in this setting, especially given several prior studies that showed no survival benefit and increased toxicity from combination therapy compared with sequential single-agent therapy in metastatic breast cancer. More studies are needed to establish the role of the AP doublet in combination with pembrolizumab in this cohort of patients, given that first-line pembrolizumab plus chemotherapy is considered the standard of care for patients with metastatic TNBC whose tumors express PD-L1.

Rugo and colleagues presented results from a randomized phase 3 study comparing 205 mg/m²oral paclitaxel plus 15 mg encequidar (a novel P-glycoprotein pump inhibitor that allows oral absorption of paclitaxel) on 3 consecutive days per week vs 175 mg/m² intravenous paclitaxel once every 3 weeks. The study enrolled 402 postmenopausal women from Latin America with metastatic breast cancer who were at least 1 year from their last taxane therapy. Oral paclitaxel plus encequidar (oPac + E) increased the confirmed tumor response compared with intravenous paclitaxel (IVpac) (36% vs 23%; P = .01). There was a trend toward improved PFS (8.4 vs 7.4 months; HR 0.768; 95.5% CI 0.584-1.01; P = .046) and OS (22.7 vs 16.5 months; HR 0.794; 95.5% CI 0.607-1.037; P = .08) with oPac + E compared to IVpac, respectively. Grade ≥3 adverse events were comparable with oPac + E and IVpac (55% vs 53%), although a lower incidence of grade 3 neuropathy (2% vs 15%) and alopecia (49% vs 62%) was noted with oPac + E compared with IVpac. A higher incidence of grade ≥ 3 gastrointestinal toxicity (nausea, vomiting, and diarrhea) and grade 4 neutropenic complications was noted in the oPac + E group. Patients with elevated baseline liver enzymes were particularly susceptible to early neutropenia and serious infections.

This study demonstrates that oral paclitaxel can be a possible alternative treatment option to intravenous paclitaxel in a select group of patients with metastatic breast cancer. High-grade neutropenia appears to be a major treatment-limiting toxicity with oPac + E. Therefore, careful patient selection and close monitoring are crucial for the successful management of this adverse event.

DESTINY-Breast04 is the first randomized clinical trial to show that targeting HER2 provides clinically meaningful benefit for patients with HER2-low metastatic breast cancer. This phase 3 study by Modi and colleagues enrolled 557 patients with hormone receptor (HR)–negative or HR-positive breast cancer and centrally confirmed HER2 low expression in those who had been previously treated with one or two prior lines of chemotherapy for metastatic breast cancer. Patients with HR-positive breast cancer were required to have endocrine therapy–refractory disease. Patients were randomized in a 2:1 ratio to receive either an antibody-drug conjugate, trastuzumab deruxtecan (T-DXd), or the physician's choice of standard chemotherapy (capecitabine, eribulin, gemcitabine, paclitaxel, or nanoparticle albumin–bound paclitaxel [nab-paclitaxel]). Among all 557 patients, T-DXd improved median progression-free survival (PFS) by 4.8 months (9.9 vs 5.1 months; hazard ratio [HR] 0.50; P < .001) and median overall survival (OS) by 6.6 months (23.4 vs 16.8 months; HR 0.64; P = .0010) compared with standard single-agent chemotherapy. Among the 494 (88.7%) HR-positive patients, the median PFS was 10.1 months in the T-DXd group and 5.4 months in the chemotherapy group (HR 0.51; P < .001). Median OS was 23.9 months and 17.5 months, respectively (HR 0.64; P = .003). The rates of grade 3 or higher adverse events were lower with T-DXd than with standard chemotherapy (52.6% vs 67.4%, respectively), although higher rates of drug-related interstitial lung disease or pneumonitis were noted in the T-DXd arm (12.1% vs 0.1%). Lung toxicity continues to be an important safety concern with T-DXd. These practice-changing results open the door to a new treatment option for a substantial group of patients with HER2-low disease and support the need to reclassify HER2-low as a new targetable subset of breast cancer, distinct from HER-negative (HER2-0), and to acquire an understanding of the clinical characteristics of and prognosis for these patients.

Tarantino and colleagues evaluated the biologic and prognostic significance of HER2-low expression in breast cancer and investigated the association between HR status and HER2-low expression. Among 5235 patients with HER2-0 invasive breast cancer, HR expression was significantly more common among HER2-low tumors than among HER2-0 tumors (90.6% vs 81.8%; P < .001). The rate of HER2-low tumors increased progressively as estrogen receptor (ER) expression increased (40.1% of ER-negative, 46.3% of ER-low, 55.2% of ER-moderate, 57.8% of ER-high, and 62.1% of ER-very high [ie, ER > 95%] tumors; P < .001). Among 675 patients receiving neoadjuvant chemotherapy, higher pathologic complete response (pCR) rates were seen among those with HER2-0 tumors (26.8% vs 16.6%; P = .002), although no statistically significant differences in pCR rates were noted between HER2-low and HER2-0 tumors when analyzed by HR and ER status. In contrast to the findings of Modi and colleagues, this analysis saw no prognostic significance in terms of survival outcomes for HER2-low expression among patients who had HR-positive or HER2-0 tumors, suggesting that HER2-low breast cancer may not be a distinct biologic subtype. Further studies are needed to clarify whether HER2-low breast cancer needs to be considered separately in practice.

Immunotherapy, particular checkpoint inhibitors, has revolutionized the treatment of many solid tumors. However, their role in HER2-positive breast cancer remains unclear. IMpassion050 is a double-blind, randomized, phase 3 study evaluating the efficacy and safety of adding atezolizumab, an anti–programmed death-ligand 1 (PD-L1) antibody, to neoadjuvant standard of care (chemotherapy + pertuzumab + trastuzumab [PH]) for high-risk, HER2-positive early breast cancer (EBC). In the study by Huober and colleagues, 454 patients with a primary tumor > 2 cm and histologically confirmed positive lymph node status (N1-3) were randomly assigned in a 1:1 ratio to the atezolizumab or placebo group with dose-dense doxorubicin or cyclophosphamide, followed by paclitaxel and PH. In the adjuvant setting, patients continued atezolizumab or placebo and PH to complete 1 year of HER2-targeted therapy; those with residual disease could switch to trastuzumab emtansine with atezolizumab or placebo. At clinical cutoff (February 5, 2021), rates of pCR in the atezolizumab group vs placebo group were similar among all patients in the study (62.4% vs 62.7%; P = .9551) and in the PD-L1–positive population (64.2% vs 72.5%; P = .1846). Treatment-related grade 3-4 adverse events occurred more frequently in the atezolizumab group compared with the placebo group, both during the neoadjuvant treatment phase (47.3% vs 42.2%) and the adjuvant treatment phase (13.4% vs 9.8%).

In summary, the phase 3 IMpassion050 trial showed no significant improvement in pCR with the addition of atezolizumab to neoadjuvant therapy in patients with high-risk, HER2-positive EBC, including those with PD-L1–positive tumors. At this time, PH and chemotherapy remain the standard of care in this patient population. Longer follow-up is needed in respect to the long-term effect of atezolizumab in this setting.

DESTINY-Breast04 is the first randomized clinical trial to show that targeting HER2 provides clinically meaningful benefit for patients with HER2-low metastatic breast cancer. This phase 3 study by Modi and colleagues enrolled 557 patients with hormone receptor (HR)–negative or HR-positive breast cancer and centrally confirmed HER2 low expression in those who had been previously treated with one or two prior lines of chemotherapy for metastatic breast cancer. Patients with HR-positive breast cancer were required to have endocrine therapy–refractory disease. Patients were randomized in a 2:1 ratio to receive either an antibody-drug conjugate, trastuzumab deruxtecan (T-DXd), or the physician's choice of standard chemotherapy (capecitabine, eribulin, gemcitabine, paclitaxel, or nanoparticle albumin–bound paclitaxel [nab-paclitaxel]). Among all 557 patients, T-DXd improved median progression-free survival (PFS) by 4.8 months (9.9 vs 5.1 months; hazard ratio [HR] 0.50; P < .001) and median overall survival (OS) by 6.6 months (23.4 vs 16.8 months; HR 0.64; P = .0010) compared with standard single-agent chemotherapy. Among the 494 (88.7%) HR-positive patients, the median PFS was 10.1 months in the T-DXd group and 5.4 months in the chemotherapy group (HR 0.51; P < .001). Median OS was 23.9 months and 17.5 months, respectively (HR 0.64; P = .003). The rates of grade 3 or higher adverse events were lower with T-DXd than with standard chemotherapy (52.6% vs 67.4%, respectively), although higher rates of drug-related interstitial lung disease or pneumonitis were noted in the T-DXd arm (12.1% vs 0.1%). Lung toxicity continues to be an important safety concern with T-DXd. These practice-changing results open the door to a new treatment option for a substantial group of patients with HER2-low disease and support the need to reclassify HER2-low as a new targetable subset of breast cancer, distinct from HER-negative (HER2-0), and to acquire an understanding of the clinical characteristics of and prognosis for these patients.

Tarantino and colleagues evaluated the biologic and prognostic significance of HER2-low expression in breast cancer and investigated the association between HR status and HER2-low expression. Among 5235 patients with HER2-0 invasive breast cancer, HR expression was significantly more common among HER2-low tumors than among HER2-0 tumors (90.6% vs 81.8%; P < .001). The rate of HER2-low tumors increased progressively as estrogen receptor (ER) expression increased (40.1% of ER-negative, 46.3% of ER-low, 55.2% of ER-moderate, 57.8% of ER-high, and 62.1% of ER-very high [ie, ER > 95%] tumors; P < .001). Among 675 patients receiving neoadjuvant chemotherapy, higher pathologic complete response (pCR) rates were seen among those with HER2-0 tumors (26.8% vs 16.6%; P = .002), although no statistically significant differences in pCR rates were noted between HER2-low and HER2-0 tumors when analyzed by HR and ER status. In contrast to the findings of Modi and colleagues, this analysis saw no prognostic significance in terms of survival outcomes for HER2-low expression among patients who had HR-positive or HER2-0 tumors, suggesting that HER2-low breast cancer may not be a distinct biologic subtype. Further studies are needed to clarify whether HER2-low breast cancer needs to be considered separately in practice.

Immunotherapy, particular checkpoint inhibitors, has revolutionized the treatment of many solid tumors. However, their role in HER2-positive breast cancer remains unclear. IMpassion050 is a double-blind, randomized, phase 3 study evaluating the efficacy and safety of adding atezolizumab, an anti–programmed death-ligand 1 (PD-L1) antibody, to neoadjuvant standard of care (chemotherapy + pertuzumab + trastuzumab [PH]) for high-risk, HER2-positive early breast cancer (EBC). In the study by Huober and colleagues, 454 patients with a primary tumor > 2 cm and histologically confirmed positive lymph node status (N1-3) were randomly assigned in a 1:1 ratio to the atezolizumab or placebo group with dose-dense doxorubicin or cyclophosphamide, followed by paclitaxel and PH. In the adjuvant setting, patients continued atezolizumab or placebo and PH to complete 1 year of HER2-targeted therapy; those with residual disease could switch to trastuzumab emtansine with atezolizumab or placebo. At clinical cutoff (February 5, 2021), rates of pCR in the atezolizumab group vs placebo group were similar among all patients in the study (62.4% vs 62.7%; P = .9551) and in the PD-L1–positive population (64.2% vs 72.5%; P = .1846). Treatment-related grade 3-4 adverse events occurred more frequently in the atezolizumab group compared with the placebo group, both during the neoadjuvant treatment phase (47.3% vs 42.2%) and the adjuvant treatment phase (13.4% vs 9.8%).

In summary, the phase 3 IMpassion050 trial showed no significant improvement in pCR with the addition of atezolizumab to neoadjuvant therapy in patients with high-risk, HER2-positive EBC, including those with PD-L1–positive tumors. At this time, PH and chemotherapy remain the standard of care in this patient population. Longer follow-up is needed in respect to the long-term effect of atezolizumab in this setting.

DESTINY-Breast04 is the first randomized clinical trial to show that targeting HER2 provides clinically meaningful benefit for patients with HER2-low metastatic breast cancer. This phase 3 study by Modi and colleagues enrolled 557 patients with hormone receptor (HR)–negative or HR-positive breast cancer and centrally confirmed HER2 low expression in those who had been previously treated with one or two prior lines of chemotherapy for metastatic breast cancer. Patients with HR-positive breast cancer were required to have endocrine therapy–refractory disease. Patients were randomized in a 2:1 ratio to receive either an antibody-drug conjugate, trastuzumab deruxtecan (T-DXd), or the physician's choice of standard chemotherapy (capecitabine, eribulin, gemcitabine, paclitaxel, or nanoparticle albumin–bound paclitaxel [nab-paclitaxel]). Among all 557 patients, T-DXd improved median progression-free survival (PFS) by 4.8 months (9.9 vs 5.1 months; hazard ratio [HR] 0.50; P < .001) and median overall survival (OS) by 6.6 months (23.4 vs 16.8 months; HR 0.64; P = .0010) compared with standard single-agent chemotherapy. Among the 494 (88.7%) HR-positive patients, the median PFS was 10.1 months in the T-DXd group and 5.4 months in the chemotherapy group (HR 0.51; P < .001). Median OS was 23.9 months and 17.5 months, respectively (HR 0.64; P = .003). The rates of grade 3 or higher adverse events were lower with T-DXd than with standard chemotherapy (52.6% vs 67.4%, respectively), although higher rates of drug-related interstitial lung disease or pneumonitis were noted in the T-DXd arm (12.1% vs 0.1%). Lung toxicity continues to be an important safety concern with T-DXd. These practice-changing results open the door to a new treatment option for a substantial group of patients with HER2-low disease and support the need to reclassify HER2-low as a new targetable subset of breast cancer, distinct from HER-negative (HER2-0), and to acquire an understanding of the clinical characteristics of and prognosis for these patients.

Tarantino and colleagues evaluated the biologic and prognostic significance of HER2-low expression in breast cancer and investigated the association between HR status and HER2-low expression. Among 5235 patients with HER2-0 invasive breast cancer, HR expression was significantly more common among HER2-low tumors than among HER2-0 tumors (90.6% vs 81.8%; P < .001). The rate of HER2-low tumors increased progressively as estrogen receptor (ER) expression increased (40.1% of ER-negative, 46.3% of ER-low, 55.2% of ER-moderate, 57.8% of ER-high, and 62.1% of ER-very high [ie, ER > 95%] tumors; P < .001). Among 675 patients receiving neoadjuvant chemotherapy, higher pathologic complete response (pCR) rates were seen among those with HER2-0 tumors (26.8% vs 16.6%; P = .002), although no statistically significant differences in pCR rates were noted between HER2-low and HER2-0 tumors when analyzed by HR and ER status. In contrast to the findings of Modi and colleagues, this analysis saw no prognostic significance in terms of survival outcomes for HER2-low expression among patients who had HR-positive or HER2-0 tumors, suggesting that HER2-low breast cancer may not be a distinct biologic subtype. Further studies are needed to clarify whether HER2-low breast cancer needs to be considered separately in practice.

Immunotherapy, particular checkpoint inhibitors, has revolutionized the treatment of many solid tumors. However, their role in HER2-positive breast cancer remains unclear. IMpassion050 is a double-blind, randomized, phase 3 study evaluating the efficacy and safety of adding atezolizumab, an anti–programmed death-ligand 1 (PD-L1) antibody, to neoadjuvant standard of care (chemotherapy + pertuzumab + trastuzumab [PH]) for high-risk, HER2-positive early breast cancer (EBC). In the study by Huober and colleagues, 454 patients with a primary tumor > 2 cm and histologically confirmed positive lymph node status (N1-3) were randomly assigned in a 1:1 ratio to the atezolizumab or placebo group with dose-dense doxorubicin or cyclophosphamide, followed by paclitaxel and PH. In the adjuvant setting, patients continued atezolizumab or placebo and PH to complete 1 year of HER2-targeted therapy; those with residual disease could switch to trastuzumab emtansine with atezolizumab or placebo. At clinical cutoff (February 5, 2021), rates of pCR in the atezolizumab group vs placebo group were similar among all patients in the study (62.4% vs 62.7%; P = .9551) and in the PD-L1–positive population (64.2% vs 72.5%; P = .1846). Treatment-related grade 3-4 adverse events occurred more frequently in the atezolizumab group compared with the placebo group, both during the neoadjuvant treatment phase (47.3% vs 42.2%) and the adjuvant treatment phase (13.4% vs 9.8%).

In summary, the phase 3 IMpassion050 trial showed no significant improvement in pCR with the addition of atezolizumab to neoadjuvant therapy in patients with high-risk, HER2-positive EBC, including those with PD-L1–positive tumors. At this time, PH and chemotherapy remain the standard of care in this patient population. Longer follow-up is needed in respect to the long-term effect of atezolizumab in this setting.