Trastuzumab emtansine (T-DM1), an antibody-drug conjugate (ADC), combines the efficacy of trastuzumab, a monoclonal antibody that targets HER2-positive breast cancer, with a cytotoxic microtubule inhibitor, DM1, which helps deliver the drug precisely to the cancer cells through receptor-mediated endocytosis, making it a potential treatment for HER2 (now erbB2)-positive patients [2,3]. This evidence concerns the gene ERBB2 and breast cancer.