The NCCN breast cancer guidelines recommend that T-DM1 is useful as preoperative/adjuvant therapy in certain circumstances in patients with HER2+ invasive breast cancer or as second-line treatment for recurrent unresectable (local or regional) or stage IV (M1) disease after pertuzumab, trastuzumab and docetaxel or paclitaxel (40). This evidence concerns the gene ERBB2 and breast cancer.