The US Food and Drug Administration-approved HER2-targeted therapies for HER2+ breast cancer include trastuzumab and pertuzumab (anti-HER2 monoclonal antibodies); lapatinib, neratinib, and tucatinib (small molecule tyrosine kinase inhibitors); and T-DM1 (an antibody–drug conjugate). This evidence concerns the gene ERBB2 and breast cancer.