A Study of T-DXd in AI-Assessed HER2-Ultralow Metastatic Breast Cancer

This is a prospective, multicenter, single-arm study designed to verify the efficacy and safety of trastuzumab deruxtecan (T-DXd) in subjects with hormone receptor-positive (HR+) unresectable and/or metastatic breast cancer who are identified as HER2-ultralow by artificial intelligence (AI)-assisted re-scoring after being manually scored as HER2-null. Eligible subjects will have progressed on at least one and up to two prior lines of endocrine therapy in the metastatic setting. Subjects are permitted to have received no more than one prior chemotherapy in the metastatic setting; however, chemotherapy must not have been the most recent treatment regimen at disease progression. Approximately 30 subjects will be enrolled at about 15 sites in China. The primary endpoint is objective response rate (ORR) by investigator assessment per RECIST 1.1.