ERBB2 and breast neoplasm: The prime example of a monoclonal antibody used in this approach is humanized anti-HER2 mAb trastuzumab (Herceptin) that plays a major role in breast cancer treatment because human epidermal growth factor receptor 2 (HER-2/neu/ErbB) gene amplification or protein overexpression occurs in 20% to 25% of breast tumors.