T-DM1 has multiple mechanisms of action, from the selective delivery of DM1 to HER2-positive tumour cells through to trastuzumab-mediated inhibition of HER2 signalling, inhibition of HER2 extracellular domain shedding and induction of antibody-dependent cell-mediated cytotoxicity (ADCC) (Fig. 2). The gene discussed is ERBB2; the disease is neoplasm.