Trastuzumab deruxtecan in previously treated HER2‐positive metastatic or unresectable breast cancer: Real‐life data from the temporary use authorization program in France

Abstract Background Early access program (formerly cohort Temporary Authorization for Use) was granted for trastuzumab deruxtecan (T‐DXd) in France based on DESTINY‐Breast01 trial which demonstrated its efficacy and safety in HER2‐positive metastatic/unresectable breast cancer after ≥2 anti‐HER2‐based regimens received at metastatic stage. Methods This multicenter real‐world early access program included HER2‐positive metastatic/unresectable breast patients pretreated with at least two lines of anti‐HER2 regimens who received T‐DXd 5.4 mg/kg intravenously in monotherapy every 3 weeks. Results Four hundred and fifty‐nine patients (median age, 58 years; hormone receptor‐positive, 67%; brain metastases, 28.1%) received T‐DXd. Before inclusion, 81.7% of patients had radiation therapy and 76.5% had undergone surgery. Median number of prior metastatic treatment lines was four (range, 2–22); 99.8% patients had received trastuzumab, 94.8% trastuzumab emtansine and 79.3% pertuzumab. Follow‐up was performed from September 30, 2020 to March 30, 2021; when the early access program stopped, the median duration of T‐DXd treatment was 3.4 (range, 0–7.8) months. In 160 patients with available tumor assessment, objective response rate was 56.7% and 12.1% had progression. In 57 patients with available brain tumor assessment, complete or partial intracranial response was reported for 35.7% patients and 5.4% had progression. A total of 17 (3.7%) patients with interstitial lung disease (ILD) was reported with no cases of ILD‐related death. Conclusions In this early access program in patients with heavily pretreated HER2‐positive metastatic/unresectable breast cancer, T‐DXd had antitumor activity with a similar response to that reported in previous clinical studies. T‐DXd was well tolerated and no new safety signals were observed.