Therapies targeting HER2 have been very successful in the treatment of breast cancer (8,9), and monoclonal antibodies (trastuzumab and pertuzumab), antibody–drug conjugates (ado-trastuzumab emtansine), and tyrosine kinase inhibitors targeting both HER1 and HER2 (lapatinib) are clinically approved for the treatment of breast cancer. The gene discussed is ERBB2; the disease is breast cancer.