ERBB2 and cancer: The homo- or hetero-dimerization of HER2 causes the autophosphorylation of the intracellular domain and triggers several downstream signaling cascades, including mitogen-activated protein kinases (MAPKs) pathway, the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/AKT pathway for mediating cell proliferation, survival, differentiation, migration, and invasion, which are thought to be the signaling pathways responsible for the transforming potential of HER2-overexpressing cancers [19–24].