Thus, in summary, T-DM1 is now indicated as a single agent in the adjuvant treatment of patients with HER2-positive (HER2+) early breast cancer who have residual invasive disease after neoadjuvant taxane and trastuzumab-based treatment, and in patients with metastatic breast cancer who previously received trastuzumab and/or a taxane, and either received previous therapy for metastatic disease or developed disease recurrence during or within six months of completing adjuvant therapy. The gene discussed is ERBB2; the disease is metastatic neoplasm.