The introduction of the humanized monoclonal antibody trastuzumab (Herceptin), which suppresses HER2-mediated signaling by binding to the extracellular domain of the HER2 protein, has dramatically improved outcomes for patients with HER2-positive breast cancer and changed the natural course of HER2-positive disease (Baselga et al., 2012). This evidence concerns the gene ERBB2 and breast cancer.