ERBB2 and cancer: T-DM1 possesses the biological properties of trastuzumab, namely HER2-signaling inhibition and antibody-dependent cell-mediated cytotoxicity, as well as the antimicrotubule activity of DM1.4 T-DM1 has been reported to overcome resistance to trastuzumab5 and lapatinib6 in HER2-amplified cancer cells, and was approved for HER2-positive metastatic breast cancer by the FDA based on the phase III EMILIA trial (NCT00829166).7,8