Modi S, Saura C, Yamashita T, et al. - Given that a response to trastuzumab deruxtecan [DS-8201; an antibody-drug conjugate containing an anti-HER2 (human epidermal growth factor receptor 2) antibody, a cleavable tetrapeptide-based linker, and a cytotoxic topoisomerase I inhibitor] (median response duration, 20.7 months) was seen in a majority of the patients with advanced HER2-positive breast cancer studied in phase 1 dose-finding study, researchers assessed trastuzumab deruxtecan in adults having pathologically documented HER2-positive metastatic breast cancer previously managed with trastuzumab emtansine in this two-part, open-label, single-group, multicenter, phase 2 study. They assessed three different doses of trastuzumab deruxtecan to ascertain a recommended dose in the first part and assessed the effectiveness as well as the safety of the recommended dose in the second part of the study. The recommended dose of trastuzumab deruxtecan (5.4 mg per kilogram of body weight) was received by 184 patients who had undergone a median of six prior treatments. Response to therapy was seen in 112 patients in the intention-to-treat analysis. The median duration of progression-free survival was found to be 16.4 months. Findings revealed durable antitumor activity of trastuzumab deruxtecan in a pretreated patient population with HER2-positive metastatic breast cancer. A subgroup of patients suffered interstitial lung disease, in addition to nausea and myelosuppression, necessitating attention to pulmonary symptoms and careful monitoring.