Currently, the American Society of Clinical Oncology (ASCO), the National Comprehensive Cancer Network and the European Society of Medical Oncology (ESMO) as well as most other treatment guidelines for breast cancer recommend the addition of anti-HER2 agents to systemic chemotherapy or endocrine therapy for the treatment of patients with early stage, locally advanced and metastatic HER2+ breast cancer. The gene discussed is ERBB2; the disease is breast cancer.