ERBB2 and breast cancer: While HER2-targeted therapies have revolutionized the management of advanced HER2-positive breast cancer since the late 1990s with approved agents including trastuzumab, pertuzumab, T-DXd, trastuzumab emtansine (T-DM1), tucatinib, lapatinib, and margetuximab, the clinical relevance of HER2 extends beyond breast cancer.