ERBB2 and breast cancer: Studies show that HER2 is not only an independent factor of poor prognosis, but also a crucial predictive factor for the response to treatment, especially for anti-HER2 targeted therapy, e.g., trastuzumab, pertuzumab, lapatinib, and Trastuzumab–emtansine, which have been demonstrated to produce responses in breast cancers showing an HER2-positive feature [4].