For example, despite a widespread overexpression of human epidermal growth factor receptor 2 (HER2) in breast cancer patients, only approximately 26% of patients with breast cancer receiving trastuzumab (an anti-HER2 monoclonal antibody) as a single agent exhibited a beneficial clinical response [10], whereas approximately 34% of patients with metastatic colorectal cancer positive for epidermal growth factor receptor (EGFR) presented stable disease upon receiving cetuximab (an anti-EGFR monoclonal antibody) as a single agent. This evidence concerns the gene EGFR and breast cancer.