Trastuzumab emtansine (T-DM1) is a novel antibody-drug conjugate that has improved overall survival in the Trastuzumab Emtansine vs. Capecitabine + Lapatinib in Patients with HER2-Positive Locally Advanced or Metastatic Breast Cancer (EMILIA) trial, which included previously treated HER2-overexpressing metastatic breast cancer and compared T-DM1 versus lapatinib plus capecitabine [35]. The gene discussed is ERBB2; the disease is breast cancer.