Importance ERRB2 (formerly HER2)–positive advanced breast cancer (ABC) remains
typically incurable with optimal treatment undefined in later lines of therapy. The chimeric
antibody margetuximab shares ERBB2 specificity with trastuzumab but incorporates an
engineered Fc region to increase immune activation. Objective To compare the clinical
efficacy of margetuximab vs trastuzumab, each with chemotherapy, in patients with
pretreated ERBB2-positive ABC. Design, Setting, and Participants The SOPHIA phase 3 …