This phase 1, open-label, dose-expansion study evaluated the safety and preliminary efficacy of trastuzumab deruxtecan (DS-8201a) in 115 patients with advanced HER2-positive breast cancer who had previously received trastuzumab emtansine. Patients received intravenous doses of 5.4 mg/kg or 6.4 mg/kg every three weeks. The confirmed objective response rate was 59.5%
