ERBB2 and breast cancer: Five human epidermal growth factor receptor 2 (HER2/ERBB2/neu)-targeted therapies are currently approved by the Food and Drug Administration (FDA) for the treatment of HER2-positive (HER2+) breast cancers: trastuzumab, pertuzumab, trastuzumab emtansine (T-DM1), lapatinib, and neratinib [1].