Eligible patients were aged ≥18 y with confirmed ERBB2-positive BC by local or optional central testing of the most recent biopsy, following 2013 ASCO testing recommendations; patients must have had progressive disease after 2 or more lines of prior ERBB2-targeted therapy, including pertuzumab, and 1 to 3 lines of nonhormonal MBC therapy. Here, ERBB2 is linked to breast cancer.