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.