This was a non-blind randomized Phase III trial comparing T-DXd and T-DM1 in 524 subjects, including patients with HER2-positive MBC with aggravation after treatment including taxane + trastuzumab, or with recurrent breast cancer within 6 months after pre- or postoperative administration of drugs including taxane + trastuzumab. This evidence concerns the gene ERBB2 and breast carcinoma.