T-DM1 was first approved as a second-line treatment for HER2+ breast cancer based on the results of the EMILIA trial, which demonstrated a significant improvement in progression-free survival (PFS) for patients treated with T-DM1 as compared to capecitabine and lapatinib (9.6 vs. 6.4 months, hazard ratio (HR) = 0.65, 95% confidence interval (CI): 0.55–0.77; p < 0.001) [7]. The gene discussed is ERBB2; the disease is breast cancer.