ERBB2 and cancer: HER2 amplification leads to the overactivation of proto-oncogenic signaling pathways, such as Phosphatidyl Inositol 3 Kinase (PI3K) and Mitogen-activated Protein Kinase (MAPK) pathways, that regulate cell proliferation, invasion, migration, angiogenesis, and apoptosis, leading to uncontrolled cancer cell growth (Yarden and Sliwkowski 2001).