ERBB2 and breast cancer: Besides trastuzumab, several HER2-directed agents have been successfully developed in the clinic; lapatinib, a reversible tyrosine kinase inhibitor (TKI) of EGFR and HER2, trastuzumab emtansine (T-DM1), an antibody-drug conjugate, and pertuzumab in association with trastuzumab have also demonstrated an OS benefit in breast cancer [8–10].