Among the various types of breast cancer, human epidermal growth factor receptor 2 (HER2)-overexpressing breast cancer, which accounts for nearly 30% of breast cancers located in either primary tumours or metastatic sites3, is known to have a poorer prognosis4, 5 and to respond poorly to chemotherapy and/or hormonal therapy6. The gene discussed is ERBB2; the disease is neoplasm.