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Study 1 Overview (Cortés et al)
Objective: To compare the efficacy and safety of trastuzumab deruxtecan with those of trastuzumab emtansine in patients with HER2-positive metastatic breast cancer previously treated with trastuzumab and taxane.
Design: Phase 3, multicenter, open-label randomized trial conducted at 169 centers and 15 countries.
Setting and participants: Eligible patients had to have unresectable or metastatic HER2-positive breast cancer that had progressed during or after treatment with trastuzumab and a taxane or had disease that progressed within 6 months after neoadjuvant or adjuvant treatment involving trastuzumab or taxane. Patients with stable or previously treated brain metastases were eligible. Patients were not eligible for the study if they had symptomatic brain metastases, prior exposure to trastuzumab emtansine, or a history of interstitial lung disease.
Intervention: Patients were randomized in a 1-to-1 fashion to receive either trastuzumab deruxtecan 5.4 mg/kg every 3 weeks or trastuzumab emtansine 3.6 mg/kg every 3 weeks. Patients were stratified according to hormone-receptor status, prior treatment with epratuzumab, and the presence or absence of visceral disease.
Main outcome measures: The primary endpoint of the study was progression-free survival as determined by an independent central review. Secondary endpoints included overall survival, overall response, and safety.
Main results: A total of 524 patients were enrolled in the study, with 261 patients randomized to trastuzumab deruxtecan and 263 patients randomized to trastuzumab emtansine. The demographic and baseline characteristics were similar between the 2 cohorts, and 60% of patients in both groups received prior epratuzumab therapy. Stable brain metastases were present in around 20% of patients in each group, and 70% of patients in each group had visceral disease. The median duration of follow-up was 16.2 months with trastuzumab deruxtecan and 15.3 months with trastuzumab emtansine.
The median progression-free survival was not reached in the trastuzumab deruxtecan group and was 6.8 months in the trastuzumab emtansine group (95% CI, 5.6-8.2). At 12 months the percentage of patients alive without disease progression was significantly larger in the trastuzumab deruxtecan group compared with the trastuzumab emtansine group. The hazard ratio for disease progression or death from any cause was 0.28 (95% CI, 0.22-0.37; P < .001). Subgroup analyses showed a benefit in progression-free survival with trastuzumab deruxtecan across all subgroups.
At the time of this analysis, the percentage of patients who were alive at 12 months was 94% with trastuzumab deruxtecan and 85.9% with trastuzumab emtansine. The response rates were significantly higher with trastuzumab deruxtecan compared with trastuzumab emtansine (79.7% vs 34.2%). A complete response was seen in 16% of patients in the trastuzumab deruxtecan arm, compared with 8.7% of patients in the trastuzumab emtansine group. The disease control rate (complete response, partial response, or stable disease) was higher in the trastuzumab deruxtecan group compared with the trastuzumab emtansine group (96.6% vs 76.8%).
Serious adverse events were reported in 19% of patients in the trastuzumab deruxtecan group and 18% of patients in the trastuzumab emtansine group. Discontinuation due to adverse events was higher in the trastuzumab deruxtecan group, with 13.6% of patients discontinuing trastuzumab deruxtecan. Grade 3 or higher adverse events were seen in 52% of patients treated with trastuzumab deruxtecan and 48% of patients treated with trastuzumab emtansine. The most commonly reported adverse event with trastuzumab deruxtecan was nausea/vomiting and fatigue. These adverse events were seen more in the trastuzumab deruxtecan group compared with the trastuzumab emtansine group. No drug-related grade 5 adverse events were reported.
In the trastuzumab deruxtecan group, 10.5% of patients receiving trastuzumab deruxtecan developed interstitial lung disease or pneumonitis. Seven patients had grade 1 events, 18 patients had grade 2 events, and 2 patients had grade 3 events. No grade 4 or 5 events were noted in either treatment group. The median time to onset of interstitial lung disease or pneumonitis in those receiving trastuzumab deruxtecan was 168 days (range, 33-507). Discontinuation of therapy due to interstitial lung disease or pneumonitis occurred in 8% of patients receiving trastuzumab deruxtecan and 1% of patients receiving trastuzumab emtansine.
Conclusion: Trastuzumab deruxtecan significantly decreases the risk of disease progression or death compared to trastuzumab emtansine in patients with HER2-positive metastatic breast cancer who have progressed on prior trastuzumab and taxane-based therapy.
Study 2 Overview (Modi et al)
Objective: To assess the efficacy of trastuzumab deruxtecan in patients with unresectable or metastatic breast cancer with low levels of HER2 expression.
Design: This was a randomized, 2-group, open-label, phase 3 trial.
Setting and participants: The trial was designed with a planned enrollment of 480 patients with hormone receptor–positive disease and 60 patients with hormone receptor–negative disease. Patients were randomized in a 2:1 ratio. Randomization was stratified according to HER2 status (immunohistochemical [IHC] 1+ vs IHC 2+/in situ hybridization [ISH] negative), number of prior lines of therapy, and hormone-receptor status. IHC scores for HER2 expression were determined through central testing. Specimens that had HER2 IHC scores of 2+ were reflexed to ISH. Specimens were considered HER2-low-expressing if they had an IHC score of 1+ or if they had an IHC score of 2+ and were ISH negative.
Eligible patients had to have received chemotherapy for metastatic disease or had disease recurrence during or within 6 months after completing adjuvant chemotherapy. Patients with hormone receptor–positive disease must have had at least 1 line of endocrine therapy. Patients were eligible if they had stable brain metastases. Patients with interstitial lung disease were excluded.
Intervention: Patients were randomized to receive trastuzumab deruxtecan 5.4 mg/kg every 3 weeks or physician’s choice of chemotherapy (capecitabine, eribulin, gemcitabine, paclitaxel, or nab-paclitaxel).
Main outcome measures: The primary endpoint was progression-free survival in patients with hormone receptor–positive disease. Secondary endpoints were progression-free survival among all patients, overall survival in hormone receptor–positive patients, and overall survival in all patients. Additional secondary endpoints included objective response rates, duration of response, and efficacy in hormone receptor–negative patients.
Main results: A total of 373 patients were assigned to the trastuzumab deruxtecan group and 184 patients were assigned to the physician’s choice chemotherapy group; 88% of patients in each cohort were hormone receptor–positive. In the physician’s choice chemotherapy group, 51% received eribulin, 20% received capecitabine, 10% received nab-paclitaxel, 10% received gemcitabine, and 8% received paclitaxel. The demographic and baseline characteristics were similar between both cohorts. The median duration of follow-up was 18.4 months.
The median progression-free survival in the hormone receptor–positive cohort was 10.1 months in the trastuzumab deruxtecan group and 5.4 months in the physician’s choice chemotherapy group (HR, 0.51; 95% CI, 0.4-0.64). Subgroup analyses revealed a benefit across all subgroups. The median progression-free survival among patients with a HER2 IHC score of 1+ and those with a HER2 IHC score of 2+/negative ISH were identical. In patients who received a prior CDK 4/6 inhibitor, the median progression-free survival was also 10 months in the trastuzumab deruxtecan group. In those who were CDK 4/6- naïve, the progression-free survival was 11.7 months. The progression-free survival in all patients was 9.9 months in the trastuzumab deruxtecan group and 5.1 months in the physician’s choice chemotherapy group (HR, 0.46; 95% CI, 0.24-0.89).
The median overall survival in the hormone receptor–positive cohort was 23.9 months in the trastuzumab deruxtecan group compared with 17.5 months in the physician’s choice chemotherapy group (HR, 0.64; 95% CI, 0.48-0.86; P = .003). The median overall survival in the entire population was 23.4 months in the trastuzumab deruxtecan group vs 16.8 months in the physician’s choice chemotherapy group. In the hormone receptor–negative cohort, the median overall survival was 18.2 months in the trastuzumab deruxtecan group and 8.3 months in the physician’s choice chemotherapy group. Complete responses were seen in 3.6% in the trastuzumab deruxtecan group and 0.6% and the physician’s choice chemotherapy group. The median duration of response was 10.7 months in the trastuzumab deruxtecan group and 6.8 months in the physician’s choice chemotherapy group.
Incidence of serious adverse events was 27% in the trastuzumab deruxtecan group and 25% in the physician’s choice chemotherapy group. Grade 3 or higher events occurred in 52% of the trastuzumab deruxtecan group and 67% of the physician’s choice chemotherapy group. Discontinuation due to adverse events occurred in 16% in the trastuzumab deruxtecan group and 18% in the physician’s choice chemotherapy group; 14 patients in the trastuzumab deruxtecan group and 5 patients in the physician’s choice chemotherapy group had an adverse event that was associated with death. Death due to pneumonitis in the trastuzumab deruxtecan group occurred in 2 patients. Drug-related interstitial lung disease or pneumonitis occurred in 45 patients who received trastuzumab deruxtecan. The majority of these events were grade 1 and grade 2. However, 3 patients had grade 5 interstitial lung disease or pneumonitis.
Conclusion: Treatment with trastuzumab deruxtecan led to a significant improvement in progression-free survival compared to physician’s choice chemotherapy in patients with HER2-low metastatic breast cancer.
Commentary
Trastuzumab deruxtecan is an antibody drug conjugate that consists of a humanized anti-HER2 monoclonal antibody linked to a topoisomerase 1 inhibitor. This antibody drug conjugate is unique compared with prior antibody drug conjugates such as trastuzumab emtansine in that it has a high drug-to-antibody ratio (~8). Furthermore, there appears to be a unique bystander effect resulting in off-target cytotoxicity to neighboring tumor cells, enhancing the efficacy of this novel therapy. Prior studies of trastuzumab deruxtecan have shown durable activity in heavily pretreated patients with metastatic HER2-positive breast cancer.1
HER2-positive breast cancer represents approximately 20% of breast cancer cases in women.2 Historically, HER2 positivity has been defined by strong HER2 expression with IHC staining (ie, score 3+) or HER2 amplification through ISH. Conversely, HER2-negative disease has historically been defined as those with IHC scores of 0 or 1+. This group represents approximately 60% of HER2-negative metastatic breast cancer patients.3 These patients have limited targeted treatment options after progressing on primary therapy. Prior data has shown that patients with low HER2 expression represent a heterogeneous population and thus, the historic categorization of HER2 status as positive or negative may in fact not adequately characterize the proportion of patients who may derive clinical benefit from HER2-directed therapies. Nevertheless, there have been no data to date that have shown improved outcomes in low HER2 expressers with anti-HER2 therapies.
The current studies add to the rapidly growing body of literature outlining the efficacy of the novel antibody drug conjugate trastuzumab deruxtecan. The implications of the data presented in these 2 studies are immediately practice changing.
In the DESTINY-Breast03 trial, Cortéz and colleagues show that trastuzumab deruxtecan therapy significantly prolongs progression-free survival compared with trastuzumab emtansine in patients with HER2-positive metastatic breast cancer who have progressed on first-line trastuzumab and taxane-based therapy. With a hazard ratio of 0.28 for disease progression or death, the efficacy of trastuzumab deruxtecan highlighted in this trial clearly makes this the standard of care in the second-line setting for patients with metastatic HER2-positive breast cancer. The overall survival in this trial was immature at the time of this analysis, and thus continued follow-up to validate the results noted here are warranted.
The DESTINY-Breast04 trial by Modi et al expands the cohort of patients who benefit from trastuzumab deruxtecan profoundly. This study defines a population of patients with HER2-low metastatic breast cancer who will now be eligible for HER2-directed therapies. These data show that therapy with trastuzumab deruxtecan leads to a significant and clinically meaningful improvement in both progression-free survival and overall survival compared with chemotherapy in patients with metastatic breast cancer with low expression of HER2. This benefit was seen in both the estrogen receptor–positive cohort as well as the entire population, including pre-treated triple-negative disease. Furthermore, this study does not define a threshold of HER2 expression by IHC that predicts benefit with trastuzumab deruxtecan. Patients with an IHC score of 1+ as well as those with a score of 2+/ISH negative both benefit to a similar extent from trastuzumab deruxtecan. Interestingly, in the DAISY trial, antitumor activity was noted with trastuzumab deruxtecan even in those without any detectable HER2 expression on IHC.4 Given the inconsistency and potential false negatives of IHC along with heterogeneous HER2 expression, further work is needed to better identify patients with low levels of HER2 expression who may benefit from this novel antibody drug conjugate. Thus, a reliable test to quantitatively assess the level of HER2 expression is needed in order to determine more accurately which patients will benefit from trastuzumab deruxtecan.
Last, trastuzumab deruxtecan has been associated with interstitial lung disease and pneumonitis. Interstitial lung disease and pneumonitis occurred in approximately 10% of patients who received trastuzumab deruxtecan in the DESTINY-Breast03 trial and about 12% of patients in the DESTINY-Breast04 trial. Most of these events were grade 1 and grade 2. Nevertheless, clinicians must be aware of this risk and monitor patients frequently for the development of pneumonitis or interstitial lung disease.
Application for Clinical Practice and System Implementation
The results of the current studies show a longer progression-free survival with trastuzumab deruxtecan in both HER2-low expressing metastatic breast cancer and HER2-positive metastatic breast cancer following taxane and trastuzumab-based therapy. These results are clearly practice changing and represent a new standard of care in these patient populations. It is incumbent upon treating oncologists to work with our pathology colleagues to assess HER2 IHC thoroughly in order to identify all potential patients who may benefit from trastuzumab deruxtecan in the metastatic setting. The continued advancement of anti-HER2 therapy will undoubtedly have a significant impact on patient outcomes going forward.
Practice Points
- With a hazard ratio of 0.28 for disease progression or death, the efficacy of trastuzumab deruxtecan highlighted in the DESTINY-Breast03 trial clearly makes this the standard of care in the second-line setting for patients with metastatic HER2-positive breast cancer.
- In the DESTINY-Breast04 trial, a significant and clinically meaningful improvement in both progression-free survival and overall survival compared with chemotherapy was seen in patients with metastatic breast cancer with low expression of HER2, including both the estrogen receptor–positive cohort as well as the entire population, including those with pre-treated triple-negative disease.
—Daniel Isaac, DO, MS
1. Modi S, Saura C, Yamashita T, et al. Trastuzumab deruxtecan in previously treated HER2-positive breast cancer. N Engl J Med. 2020;382(7):610-621. doi:10.1056/NEJMoa1914510
2. National Cancer Institute. Cancer stat facts. female breast cancer. Accessed July 25, 2022. https://seer.cancer.gov/statfacts/html/breast.html
3. Schettini F, Chic N, Braso-Maristany F, et al. Clinical, pathological and PAM50 gene expression features of HER2-low breast cancer. NPJ Breast Cancer. 2021;7(`1):1. doi:10.1038/s41523-020-00208-2
4. Dieras VDE, Deluche E, Lusque A, et al. Trastuzumab deruxtecan for advanced breast cancer patients, regardless of HER2 status: a phase II study with biomarkers analysis. In: Proceedings of Abstracts of the 2021 San Antonio Breast Cancer Symposium, December 7-10, 2021. San Antonio: American Association for Cancer Research, 2021. Abstract.
Study 1 Overview (Cortés et al)
Objective: To compare the efficacy and safety of trastuzumab deruxtecan with those of trastuzumab emtansine in patients with HER2-positive metastatic breast cancer previously treated with trastuzumab and taxane.
Design: Phase 3, multicenter, open-label randomized trial conducted at 169 centers and 15 countries.
Setting and participants: Eligible patients had to have unresectable or metastatic HER2-positive breast cancer that had progressed during or after treatment with trastuzumab and a taxane or had disease that progressed within 6 months after neoadjuvant or adjuvant treatment involving trastuzumab or taxane. Patients with stable or previously treated brain metastases were eligible. Patients were not eligible for the study if they had symptomatic brain metastases, prior exposure to trastuzumab emtansine, or a history of interstitial lung disease.
Intervention: Patients were randomized in a 1-to-1 fashion to receive either trastuzumab deruxtecan 5.4 mg/kg every 3 weeks or trastuzumab emtansine 3.6 mg/kg every 3 weeks. Patients were stratified according to hormone-receptor status, prior treatment with epratuzumab, and the presence or absence of visceral disease.
Main outcome measures: The primary endpoint of the study was progression-free survival as determined by an independent central review. Secondary endpoints included overall survival, overall response, and safety.
Main results: A total of 524 patients were enrolled in the study, with 261 patients randomized to trastuzumab deruxtecan and 263 patients randomized to trastuzumab emtansine. The demographic and baseline characteristics were similar between the 2 cohorts, and 60% of patients in both groups received prior epratuzumab therapy. Stable brain metastases were present in around 20% of patients in each group, and 70% of patients in each group had visceral disease. The median duration of follow-up was 16.2 months with trastuzumab deruxtecan and 15.3 months with trastuzumab emtansine.
The median progression-free survival was not reached in the trastuzumab deruxtecan group and was 6.8 months in the trastuzumab emtansine group (95% CI, 5.6-8.2). At 12 months the percentage of patients alive without disease progression was significantly larger in the trastuzumab deruxtecan group compared with the trastuzumab emtansine group. The hazard ratio for disease progression or death from any cause was 0.28 (95% CI, 0.22-0.37; P < .001). Subgroup analyses showed a benefit in progression-free survival with trastuzumab deruxtecan across all subgroups.
At the time of this analysis, the percentage of patients who were alive at 12 months was 94% with trastuzumab deruxtecan and 85.9% with trastuzumab emtansine. The response rates were significantly higher with trastuzumab deruxtecan compared with trastuzumab emtansine (79.7% vs 34.2%). A complete response was seen in 16% of patients in the trastuzumab deruxtecan arm, compared with 8.7% of patients in the trastuzumab emtansine group. The disease control rate (complete response, partial response, or stable disease) was higher in the trastuzumab deruxtecan group compared with the trastuzumab emtansine group (96.6% vs 76.8%).
Serious adverse events were reported in 19% of patients in the trastuzumab deruxtecan group and 18% of patients in the trastuzumab emtansine group. Discontinuation due to adverse events was higher in the trastuzumab deruxtecan group, with 13.6% of patients discontinuing trastuzumab deruxtecan. Grade 3 or higher adverse events were seen in 52% of patients treated with trastuzumab deruxtecan and 48% of patients treated with trastuzumab emtansine. The most commonly reported adverse event with trastuzumab deruxtecan was nausea/vomiting and fatigue. These adverse events were seen more in the trastuzumab deruxtecan group compared with the trastuzumab emtansine group. No drug-related grade 5 adverse events were reported.
In the trastuzumab deruxtecan group, 10.5% of patients receiving trastuzumab deruxtecan developed interstitial lung disease or pneumonitis. Seven patients had grade 1 events, 18 patients had grade 2 events, and 2 patients had grade 3 events. No grade 4 or 5 events were noted in either treatment group. The median time to onset of interstitial lung disease or pneumonitis in those receiving trastuzumab deruxtecan was 168 days (range, 33-507). Discontinuation of therapy due to interstitial lung disease or pneumonitis occurred in 8% of patients receiving trastuzumab deruxtecan and 1% of patients receiving trastuzumab emtansine.
Conclusion: Trastuzumab deruxtecan significantly decreases the risk of disease progression or death compared to trastuzumab emtansine in patients with HER2-positive metastatic breast cancer who have progressed on prior trastuzumab and taxane-based therapy.
Study 2 Overview (Modi et al)
Objective: To assess the efficacy of trastuzumab deruxtecan in patients with unresectable or metastatic breast cancer with low levels of HER2 expression.
Design: This was a randomized, 2-group, open-label, phase 3 trial.
Setting and participants: The trial was designed with a planned enrollment of 480 patients with hormone receptor–positive disease and 60 patients with hormone receptor–negative disease. Patients were randomized in a 2:1 ratio. Randomization was stratified according to HER2 status (immunohistochemical [IHC] 1+ vs IHC 2+/in situ hybridization [ISH] negative), number of prior lines of therapy, and hormone-receptor status. IHC scores for HER2 expression were determined through central testing. Specimens that had HER2 IHC scores of 2+ were reflexed to ISH. Specimens were considered HER2-low-expressing if they had an IHC score of 1+ or if they had an IHC score of 2+ and were ISH negative.
Eligible patients had to have received chemotherapy for metastatic disease or had disease recurrence during or within 6 months after completing adjuvant chemotherapy. Patients with hormone receptor–positive disease must have had at least 1 line of endocrine therapy. Patients were eligible if they had stable brain metastases. Patients with interstitial lung disease were excluded.
Intervention: Patients were randomized to receive trastuzumab deruxtecan 5.4 mg/kg every 3 weeks or physician’s choice of chemotherapy (capecitabine, eribulin, gemcitabine, paclitaxel, or nab-paclitaxel).
Main outcome measures: The primary endpoint was progression-free survival in patients with hormone receptor–positive disease. Secondary endpoints were progression-free survival among all patients, overall survival in hormone receptor–positive patients, and overall survival in all patients. Additional secondary endpoints included objective response rates, duration of response, and efficacy in hormone receptor–negative patients.
Main results: A total of 373 patients were assigned to the trastuzumab deruxtecan group and 184 patients were assigned to the physician’s choice chemotherapy group; 88% of patients in each cohort were hormone receptor–positive. In the physician’s choice chemotherapy group, 51% received eribulin, 20% received capecitabine, 10% received nab-paclitaxel, 10% received gemcitabine, and 8% received paclitaxel. The demographic and baseline characteristics were similar between both cohorts. The median duration of follow-up was 18.4 months.
The median progression-free survival in the hormone receptor–positive cohort was 10.1 months in the trastuzumab deruxtecan group and 5.4 months in the physician’s choice chemotherapy group (HR, 0.51; 95% CI, 0.4-0.64). Subgroup analyses revealed a benefit across all subgroups. The median progression-free survival among patients with a HER2 IHC score of 1+ and those with a HER2 IHC score of 2+/negative ISH were identical. In patients who received a prior CDK 4/6 inhibitor, the median progression-free survival was also 10 months in the trastuzumab deruxtecan group. In those who were CDK 4/6- naïve, the progression-free survival was 11.7 months. The progression-free survival in all patients was 9.9 months in the trastuzumab deruxtecan group and 5.1 months in the physician’s choice chemotherapy group (HR, 0.46; 95% CI, 0.24-0.89).
The median overall survival in the hormone receptor–positive cohort was 23.9 months in the trastuzumab deruxtecan group compared with 17.5 months in the physician’s choice chemotherapy group (HR, 0.64; 95% CI, 0.48-0.86; P = .003). The median overall survival in the entire population was 23.4 months in the trastuzumab deruxtecan group vs 16.8 months in the physician’s choice chemotherapy group. In the hormone receptor–negative cohort, the median overall survival was 18.2 months in the trastuzumab deruxtecan group and 8.3 months in the physician’s choice chemotherapy group. Complete responses were seen in 3.6% in the trastuzumab deruxtecan group and 0.6% and the physician’s choice chemotherapy group. The median duration of response was 10.7 months in the trastuzumab deruxtecan group and 6.8 months in the physician’s choice chemotherapy group.
Incidence of serious adverse events was 27% in the trastuzumab deruxtecan group and 25% in the physician’s choice chemotherapy group. Grade 3 or higher events occurred in 52% of the trastuzumab deruxtecan group and 67% of the physician’s choice chemotherapy group. Discontinuation due to adverse events occurred in 16% in the trastuzumab deruxtecan group and 18% in the physician’s choice chemotherapy group; 14 patients in the trastuzumab deruxtecan group and 5 patients in the physician’s choice chemotherapy group had an adverse event that was associated with death. Death due to pneumonitis in the trastuzumab deruxtecan group occurred in 2 patients. Drug-related interstitial lung disease or pneumonitis occurred in 45 patients who received trastuzumab deruxtecan. The majority of these events were grade 1 and grade 2. However, 3 patients had grade 5 interstitial lung disease or pneumonitis.
Conclusion: Treatment with trastuzumab deruxtecan led to a significant improvement in progression-free survival compared to physician’s choice chemotherapy in patients with HER2-low metastatic breast cancer.
Commentary
Trastuzumab deruxtecan is an antibody drug conjugate that consists of a humanized anti-HER2 monoclonal antibody linked to a topoisomerase 1 inhibitor. This antibody drug conjugate is unique compared with prior antibody drug conjugates such as trastuzumab emtansine in that it has a high drug-to-antibody ratio (~8). Furthermore, there appears to be a unique bystander effect resulting in off-target cytotoxicity to neighboring tumor cells, enhancing the efficacy of this novel therapy. Prior studies of trastuzumab deruxtecan have shown durable activity in heavily pretreated patients with metastatic HER2-positive breast cancer.1
HER2-positive breast cancer represents approximately 20% of breast cancer cases in women.2 Historically, HER2 positivity has been defined by strong HER2 expression with IHC staining (ie, score 3+) or HER2 amplification through ISH. Conversely, HER2-negative disease has historically been defined as those with IHC scores of 0 or 1+. This group represents approximately 60% of HER2-negative metastatic breast cancer patients.3 These patients have limited targeted treatment options after progressing on primary therapy. Prior data has shown that patients with low HER2 expression represent a heterogeneous population and thus, the historic categorization of HER2 status as positive or negative may in fact not adequately characterize the proportion of patients who may derive clinical benefit from HER2-directed therapies. Nevertheless, there have been no data to date that have shown improved outcomes in low HER2 expressers with anti-HER2 therapies.
The current studies add to the rapidly growing body of literature outlining the efficacy of the novel antibody drug conjugate trastuzumab deruxtecan. The implications of the data presented in these 2 studies are immediately practice changing.
In the DESTINY-Breast03 trial, Cortéz and colleagues show that trastuzumab deruxtecan therapy significantly prolongs progression-free survival compared with trastuzumab emtansine in patients with HER2-positive metastatic breast cancer who have progressed on first-line trastuzumab and taxane-based therapy. With a hazard ratio of 0.28 for disease progression or death, the efficacy of trastuzumab deruxtecan highlighted in this trial clearly makes this the standard of care in the second-line setting for patients with metastatic HER2-positive breast cancer. The overall survival in this trial was immature at the time of this analysis, and thus continued follow-up to validate the results noted here are warranted.
The DESTINY-Breast04 trial by Modi et al expands the cohort of patients who benefit from trastuzumab deruxtecan profoundly. This study defines a population of patients with HER2-low metastatic breast cancer who will now be eligible for HER2-directed therapies. These data show that therapy with trastuzumab deruxtecan leads to a significant and clinically meaningful improvement in both progression-free survival and overall survival compared with chemotherapy in patients with metastatic breast cancer with low expression of HER2. This benefit was seen in both the estrogen receptor–positive cohort as well as the entire population, including pre-treated triple-negative disease. Furthermore, this study does not define a threshold of HER2 expression by IHC that predicts benefit with trastuzumab deruxtecan. Patients with an IHC score of 1+ as well as those with a score of 2+/ISH negative both benefit to a similar extent from trastuzumab deruxtecan. Interestingly, in the DAISY trial, antitumor activity was noted with trastuzumab deruxtecan even in those without any detectable HER2 expression on IHC.4 Given the inconsistency and potential false negatives of IHC along with heterogeneous HER2 expression, further work is needed to better identify patients with low levels of HER2 expression who may benefit from this novel antibody drug conjugate. Thus, a reliable test to quantitatively assess the level of HER2 expression is needed in order to determine more accurately which patients will benefit from trastuzumab deruxtecan.
Last, trastuzumab deruxtecan has been associated with interstitial lung disease and pneumonitis. Interstitial lung disease and pneumonitis occurred in approximately 10% of patients who received trastuzumab deruxtecan in the DESTINY-Breast03 trial and about 12% of patients in the DESTINY-Breast04 trial. Most of these events were grade 1 and grade 2. Nevertheless, clinicians must be aware of this risk and monitor patients frequently for the development of pneumonitis or interstitial lung disease.
Application for Clinical Practice and System Implementation
The results of the current studies show a longer progression-free survival with trastuzumab deruxtecan in both HER2-low expressing metastatic breast cancer and HER2-positive metastatic breast cancer following taxane and trastuzumab-based therapy. These results are clearly practice changing and represent a new standard of care in these patient populations. It is incumbent upon treating oncologists to work with our pathology colleagues to assess HER2 IHC thoroughly in order to identify all potential patients who may benefit from trastuzumab deruxtecan in the metastatic setting. The continued advancement of anti-HER2 therapy will undoubtedly have a significant impact on patient outcomes going forward.
Practice Points
- With a hazard ratio of 0.28 for disease progression or death, the efficacy of trastuzumab deruxtecan highlighted in the DESTINY-Breast03 trial clearly makes this the standard of care in the second-line setting for patients with metastatic HER2-positive breast cancer.
- In the DESTINY-Breast04 trial, a significant and clinically meaningful improvement in both progression-free survival and overall survival compared with chemotherapy was seen in patients with metastatic breast cancer with low expression of HER2, including both the estrogen receptor–positive cohort as well as the entire population, including those with pre-treated triple-negative disease.
—Daniel Isaac, DO, MS
Study 1 Overview (Cortés et al)
Objective: To compare the efficacy and safety of trastuzumab deruxtecan with those of trastuzumab emtansine in patients with HER2-positive metastatic breast cancer previously treated with trastuzumab and taxane.
Design: Phase 3, multicenter, open-label randomized trial conducted at 169 centers and 15 countries.
Setting and participants: Eligible patients had to have unresectable or metastatic HER2-positive breast cancer that had progressed during or after treatment with trastuzumab and a taxane or had disease that progressed within 6 months after neoadjuvant or adjuvant treatment involving trastuzumab or taxane. Patients with stable or previously treated brain metastases were eligible. Patients were not eligible for the study if they had symptomatic brain metastases, prior exposure to trastuzumab emtansine, or a history of interstitial lung disease.
Intervention: Patients were randomized in a 1-to-1 fashion to receive either trastuzumab deruxtecan 5.4 mg/kg every 3 weeks or trastuzumab emtansine 3.6 mg/kg every 3 weeks. Patients were stratified according to hormone-receptor status, prior treatment with epratuzumab, and the presence or absence of visceral disease.
Main outcome measures: The primary endpoint of the study was progression-free survival as determined by an independent central review. Secondary endpoints included overall survival, overall response, and safety.
Main results: A total of 524 patients were enrolled in the study, with 261 patients randomized to trastuzumab deruxtecan and 263 patients randomized to trastuzumab emtansine. The demographic and baseline characteristics were similar between the 2 cohorts, and 60% of patients in both groups received prior epratuzumab therapy. Stable brain metastases were present in around 20% of patients in each group, and 70% of patients in each group had visceral disease. The median duration of follow-up was 16.2 months with trastuzumab deruxtecan and 15.3 months with trastuzumab emtansine.
The median progression-free survival was not reached in the trastuzumab deruxtecan group and was 6.8 months in the trastuzumab emtansine group (95% CI, 5.6-8.2). At 12 months the percentage of patients alive without disease progression was significantly larger in the trastuzumab deruxtecan group compared with the trastuzumab emtansine group. The hazard ratio for disease progression or death from any cause was 0.28 (95% CI, 0.22-0.37; P < .001). Subgroup analyses showed a benefit in progression-free survival with trastuzumab deruxtecan across all subgroups.
At the time of this analysis, the percentage of patients who were alive at 12 months was 94% with trastuzumab deruxtecan and 85.9% with trastuzumab emtansine. The response rates were significantly higher with trastuzumab deruxtecan compared with trastuzumab emtansine (79.7% vs 34.2%). A complete response was seen in 16% of patients in the trastuzumab deruxtecan arm, compared with 8.7% of patients in the trastuzumab emtansine group. The disease control rate (complete response, partial response, or stable disease) was higher in the trastuzumab deruxtecan group compared with the trastuzumab emtansine group (96.6% vs 76.8%).
Serious adverse events were reported in 19% of patients in the trastuzumab deruxtecan group and 18% of patients in the trastuzumab emtansine group. Discontinuation due to adverse events was higher in the trastuzumab deruxtecan group, with 13.6% of patients discontinuing trastuzumab deruxtecan. Grade 3 or higher adverse events were seen in 52% of patients treated with trastuzumab deruxtecan and 48% of patients treated with trastuzumab emtansine. The most commonly reported adverse event with trastuzumab deruxtecan was nausea/vomiting and fatigue. These adverse events were seen more in the trastuzumab deruxtecan group compared with the trastuzumab emtansine group. No drug-related grade 5 adverse events were reported.
In the trastuzumab deruxtecan group, 10.5% of patients receiving trastuzumab deruxtecan developed interstitial lung disease or pneumonitis. Seven patients had grade 1 events, 18 patients had grade 2 events, and 2 patients had grade 3 events. No grade 4 or 5 events were noted in either treatment group. The median time to onset of interstitial lung disease or pneumonitis in those receiving trastuzumab deruxtecan was 168 days (range, 33-507). Discontinuation of therapy due to interstitial lung disease or pneumonitis occurred in 8% of patients receiving trastuzumab deruxtecan and 1% of patients receiving trastuzumab emtansine.
Conclusion: Trastuzumab deruxtecan significantly decreases the risk of disease progression or death compared to trastuzumab emtansine in patients with HER2-positive metastatic breast cancer who have progressed on prior trastuzumab and taxane-based therapy.
Study 2 Overview (Modi et al)
Objective: To assess the efficacy of trastuzumab deruxtecan in patients with unresectable or metastatic breast cancer with low levels of HER2 expression.
Design: This was a randomized, 2-group, open-label, phase 3 trial.
Setting and participants: The trial was designed with a planned enrollment of 480 patients with hormone receptor–positive disease and 60 patients with hormone receptor–negative disease. Patients were randomized in a 2:1 ratio. Randomization was stratified according to HER2 status (immunohistochemical [IHC] 1+ vs IHC 2+/in situ hybridization [ISH] negative), number of prior lines of therapy, and hormone-receptor status. IHC scores for HER2 expression were determined through central testing. Specimens that had HER2 IHC scores of 2+ were reflexed to ISH. Specimens were considered HER2-low-expressing if they had an IHC score of 1+ or if they had an IHC score of 2+ and were ISH negative.
Eligible patients had to have received chemotherapy for metastatic disease or had disease recurrence during or within 6 months after completing adjuvant chemotherapy. Patients with hormone receptor–positive disease must have had at least 1 line of endocrine therapy. Patients were eligible if they had stable brain metastases. Patients with interstitial lung disease were excluded.
Intervention: Patients were randomized to receive trastuzumab deruxtecan 5.4 mg/kg every 3 weeks or physician’s choice of chemotherapy (capecitabine, eribulin, gemcitabine, paclitaxel, or nab-paclitaxel).
Main outcome measures: The primary endpoint was progression-free survival in patients with hormone receptor–positive disease. Secondary endpoints were progression-free survival among all patients, overall survival in hormone receptor–positive patients, and overall survival in all patients. Additional secondary endpoints included objective response rates, duration of response, and efficacy in hormone receptor–negative patients.
Main results: A total of 373 patients were assigned to the trastuzumab deruxtecan group and 184 patients were assigned to the physician’s choice chemotherapy group; 88% of patients in each cohort were hormone receptor–positive. In the physician’s choice chemotherapy group, 51% received eribulin, 20% received capecitabine, 10% received nab-paclitaxel, 10% received gemcitabine, and 8% received paclitaxel. The demographic and baseline characteristics were similar between both cohorts. The median duration of follow-up was 18.4 months.
The median progression-free survival in the hormone receptor–positive cohort was 10.1 months in the trastuzumab deruxtecan group and 5.4 months in the physician’s choice chemotherapy group (HR, 0.51; 95% CI, 0.4-0.64). Subgroup analyses revealed a benefit across all subgroups. The median progression-free survival among patients with a HER2 IHC score of 1+ and those with a HER2 IHC score of 2+/negative ISH were identical. In patients who received a prior CDK 4/6 inhibitor, the median progression-free survival was also 10 months in the trastuzumab deruxtecan group. In those who were CDK 4/6- naïve, the progression-free survival was 11.7 months. The progression-free survival in all patients was 9.9 months in the trastuzumab deruxtecan group and 5.1 months in the physician’s choice chemotherapy group (HR, 0.46; 95% CI, 0.24-0.89).
The median overall survival in the hormone receptor–positive cohort was 23.9 months in the trastuzumab deruxtecan group compared with 17.5 months in the physician’s choice chemotherapy group (HR, 0.64; 95% CI, 0.48-0.86; P = .003). The median overall survival in the entire population was 23.4 months in the trastuzumab deruxtecan group vs 16.8 months in the physician’s choice chemotherapy group. In the hormone receptor–negative cohort, the median overall survival was 18.2 months in the trastuzumab deruxtecan group and 8.3 months in the physician’s choice chemotherapy group. Complete responses were seen in 3.6% in the trastuzumab deruxtecan group and 0.6% and the physician’s choice chemotherapy group. The median duration of response was 10.7 months in the trastuzumab deruxtecan group and 6.8 months in the physician’s choice chemotherapy group.
Incidence of serious adverse events was 27% in the trastuzumab deruxtecan group and 25% in the physician’s choice chemotherapy group. Grade 3 or higher events occurred in 52% of the trastuzumab deruxtecan group and 67% of the physician’s choice chemotherapy group. Discontinuation due to adverse events occurred in 16% in the trastuzumab deruxtecan group and 18% in the physician’s choice chemotherapy group; 14 patients in the trastuzumab deruxtecan group and 5 patients in the physician’s choice chemotherapy group had an adverse event that was associated with death. Death due to pneumonitis in the trastuzumab deruxtecan group occurred in 2 patients. Drug-related interstitial lung disease or pneumonitis occurred in 45 patients who received trastuzumab deruxtecan. The majority of these events were grade 1 and grade 2. However, 3 patients had grade 5 interstitial lung disease or pneumonitis.
Conclusion: Treatment with trastuzumab deruxtecan led to a significant improvement in progression-free survival compared to physician’s choice chemotherapy in patients with HER2-low metastatic breast cancer.
Commentary
Trastuzumab deruxtecan is an antibody drug conjugate that consists of a humanized anti-HER2 monoclonal antibody linked to a topoisomerase 1 inhibitor. This antibody drug conjugate is unique compared with prior antibody drug conjugates such as trastuzumab emtansine in that it has a high drug-to-antibody ratio (~8). Furthermore, there appears to be a unique bystander effect resulting in off-target cytotoxicity to neighboring tumor cells, enhancing the efficacy of this novel therapy. Prior studies of trastuzumab deruxtecan have shown durable activity in heavily pretreated patients with metastatic HER2-positive breast cancer.1
HER2-positive breast cancer represents approximately 20% of breast cancer cases in women.2 Historically, HER2 positivity has been defined by strong HER2 expression with IHC staining (ie, score 3+) or HER2 amplification through ISH. Conversely, HER2-negative disease has historically been defined as those with IHC scores of 0 or 1+. This group represents approximately 60% of HER2-negative metastatic breast cancer patients.3 These patients have limited targeted treatment options after progressing on primary therapy. Prior data has shown that patients with low HER2 expression represent a heterogeneous population and thus, the historic categorization of HER2 status as positive or negative may in fact not adequately characterize the proportion of patients who may derive clinical benefit from HER2-directed therapies. Nevertheless, there have been no data to date that have shown improved outcomes in low HER2 expressers with anti-HER2 therapies.
The current studies add to the rapidly growing body of literature outlining the efficacy of the novel antibody drug conjugate trastuzumab deruxtecan. The implications of the data presented in these 2 studies are immediately practice changing.
In the DESTINY-Breast03 trial, Cortéz and colleagues show that trastuzumab deruxtecan therapy significantly prolongs progression-free survival compared with trastuzumab emtansine in patients with HER2-positive metastatic breast cancer who have progressed on first-line trastuzumab and taxane-based therapy. With a hazard ratio of 0.28 for disease progression or death, the efficacy of trastuzumab deruxtecan highlighted in this trial clearly makes this the standard of care in the second-line setting for patients with metastatic HER2-positive breast cancer. The overall survival in this trial was immature at the time of this analysis, and thus continued follow-up to validate the results noted here are warranted.
The DESTINY-Breast04 trial by Modi et al expands the cohort of patients who benefit from trastuzumab deruxtecan profoundly. This study defines a population of patients with HER2-low metastatic breast cancer who will now be eligible for HER2-directed therapies. These data show that therapy with trastuzumab deruxtecan leads to a significant and clinically meaningful improvement in both progression-free survival and overall survival compared with chemotherapy in patients with metastatic breast cancer with low expression of HER2. This benefit was seen in both the estrogen receptor–positive cohort as well as the entire population, including pre-treated triple-negative disease. Furthermore, this study does not define a threshold of HER2 expression by IHC that predicts benefit with trastuzumab deruxtecan. Patients with an IHC score of 1+ as well as those with a score of 2+/ISH negative both benefit to a similar extent from trastuzumab deruxtecan. Interestingly, in the DAISY trial, antitumor activity was noted with trastuzumab deruxtecan even in those without any detectable HER2 expression on IHC.4 Given the inconsistency and potential false negatives of IHC along with heterogeneous HER2 expression, further work is needed to better identify patients with low levels of HER2 expression who may benefit from this novel antibody drug conjugate. Thus, a reliable test to quantitatively assess the level of HER2 expression is needed in order to determine more accurately which patients will benefit from trastuzumab deruxtecan.
Last, trastuzumab deruxtecan has been associated with interstitial lung disease and pneumonitis. Interstitial lung disease and pneumonitis occurred in approximately 10% of patients who received trastuzumab deruxtecan in the DESTINY-Breast03 trial and about 12% of patients in the DESTINY-Breast04 trial. Most of these events were grade 1 and grade 2. Nevertheless, clinicians must be aware of this risk and monitor patients frequently for the development of pneumonitis or interstitial lung disease.
Application for Clinical Practice and System Implementation
The results of the current studies show a longer progression-free survival with trastuzumab deruxtecan in both HER2-low expressing metastatic breast cancer and HER2-positive metastatic breast cancer following taxane and trastuzumab-based therapy. These results are clearly practice changing and represent a new standard of care in these patient populations. It is incumbent upon treating oncologists to work with our pathology colleagues to assess HER2 IHC thoroughly in order to identify all potential patients who may benefit from trastuzumab deruxtecan in the metastatic setting. The continued advancement of anti-HER2 therapy will undoubtedly have a significant impact on patient outcomes going forward.
Practice Points
- With a hazard ratio of 0.28 for disease progression or death, the efficacy of trastuzumab deruxtecan highlighted in the DESTINY-Breast03 trial clearly makes this the standard of care in the second-line setting for patients with metastatic HER2-positive breast cancer.
- In the DESTINY-Breast04 trial, a significant and clinically meaningful improvement in both progression-free survival and overall survival compared with chemotherapy was seen in patients with metastatic breast cancer with low expression of HER2, including both the estrogen receptor–positive cohort as well as the entire population, including those with pre-treated triple-negative disease.
—Daniel Isaac, DO, MS
1. Modi S, Saura C, Yamashita T, et al. Trastuzumab deruxtecan in previously treated HER2-positive breast cancer. N Engl J Med. 2020;382(7):610-621. doi:10.1056/NEJMoa1914510
2. National Cancer Institute. Cancer stat facts. female breast cancer. Accessed July 25, 2022. https://seer.cancer.gov/statfacts/html/breast.html
3. Schettini F, Chic N, Braso-Maristany F, et al. Clinical, pathological and PAM50 gene expression features of HER2-low breast cancer. NPJ Breast Cancer. 2021;7(`1):1. doi:10.1038/s41523-020-00208-2
4. Dieras VDE, Deluche E, Lusque A, et al. Trastuzumab deruxtecan for advanced breast cancer patients, regardless of HER2 status: a phase II study with biomarkers analysis. In: Proceedings of Abstracts of the 2021 San Antonio Breast Cancer Symposium, December 7-10, 2021. San Antonio: American Association for Cancer Research, 2021. Abstract.
1. Modi S, Saura C, Yamashita T, et al. Trastuzumab deruxtecan in previously treated HER2-positive breast cancer. N Engl J Med. 2020;382(7):610-621. doi:10.1056/NEJMoa1914510
2. National Cancer Institute. Cancer stat facts. female breast cancer. Accessed July 25, 2022. https://seer.cancer.gov/statfacts/html/breast.html
3. Schettini F, Chic N, Braso-Maristany F, et al. Clinical, pathological and PAM50 gene expression features of HER2-low breast cancer. NPJ Breast Cancer. 2021;7(`1):1. doi:10.1038/s41523-020-00208-2
4. Dieras VDE, Deluche E, Lusque A, et al. Trastuzumab deruxtecan for advanced breast cancer patients, regardless of HER2 status: a phase II study with biomarkers analysis. In: Proceedings of Abstracts of the 2021 San Antonio Breast Cancer Symposium, December 7-10, 2021. San Antonio: American Association for Cancer Research, 2021. Abstract.