ERBB2 and cancer: Recently, two additional HER2 blocking agents became part of our therapeutic armamentarium: trastuzumab-DM1, an antibody-drug conjugate, delivering potent cytotoxic chemotherapy to HER2-overexpressing cancer cells, while retaining the biologic actions of trastuzumab; and pertuzumab, an anti-HER2 monoclonal antibody, which when coupled with trastuzumab achieves a more thorough HER2 blockade, capitalizing on the concept of dual HER2 blockade [23, 24].