ERBB2 and breast cancer: Ado-trastuzumab (T-DM1), an antibody-drug conjugate of trastuzumab and a cytotoxic microtubule-inhibitory agent, emtansine (DM1), has been shown to prolong PFS when studied in second-line (EMILIA) and later-lines of therapy (TH3RESA) in metastatic HER2-positive breast cancer [9, 10].