This is a randomized controlled, 2-arm, open-label, multicenter phase III study to assess the efficacy and safety of DB-1303/BNT323 versus Trastuzumab Emtansine (T-DM1) in patients with human epidermal growth factor receptor 2 (HER2) -positive unresectable/metastatic breast cancer who have been treated with trastuzumab and taxanes. Approximately 224 patients with unresectable or metastatic HER2-positive breast cancer will be randomized 1:1 to receive DB-1303/BNT323 or T-DM1, respectively.
