ERBB2 and breast cancer: Although HER2-targeted therapeutics, such as the administration of an inhibitory humanized monoclonal antibody against HER2 (e.g., trastuzumab), are effective for HER2-positive breast cancer patients, the development of trastuzumab resistance with its long-term administration often poses a major challenge (Esteva et al, 2002; Nahta et al, 2006; Dokmanovic et al, 2011).