ERBB2 and breast cancer: Human epidermal growth factor receptor 2 (HER2/neu) is an oncogene involved in abnormal cell growth in breast cancer and is a target for the humanised monoclonal antibody (mAb) trastuzumab (Herceptin) [23], which was approved by the US Food and Drug Administration for the treatment of HER2/neu-overexpressing breast tumours.