For patients with HER2+ early breast cancer in whom residual invasive disease is detected pathologically in the surgical specimen of the breast or axillary lymph nodes after completion of neoadjuvant trastuzumab + pertuzumab + chemotherapy, the standard of care is to treat with trastuzumab emtansine (T-DM1) for 14 cycles in the adjuvant setting (strong recommendation). The gene discussed is ERBB2; the disease is breast carcinoma.