Regulatory approval for T-DM1 was based on the pivotal EMILIA study, which randomised 991 patients with previously treated (taxane plus trastuzumab) locally advanced unresectable or metastatic HER2-positive breast cancer to T-DM1, or lapatinib plus capecitabine, the standard of care at that time. The gene discussed is ERBB2; the disease is breast cancer.