ERBB2, also named c-erb B2, CD340, HER-2, HER-2/neu, HER2, NEU and TKR1, encodes a member of the epidermal growth factor (EGF) receptor family of receptor tyrosine kinases. It has no ligand binding domain of its own and therefore cannot bind growth factors. However, it does bind tightly to other ligand-bound EGF receptor family members to form a heterodimer, stabilizing ligand binding and enhancing kinase-mediated activation of downstream signalling pathways, such as those involving mitogen-activated protein kinase and phosphatidylinositol-3 kinase. Amplification and/or overexpression of ERBB2 have been reported in numerous cancers, including breast and ovarian tumors. There are many forms of breast cancer based in part on genetic characteristics, such as HER2(ERBB2)-positive and HER2(ERBB2)-negative. Each form of breast cancer has a different prognosis. ERBB2 is an essential component of a neuregulin-receptor complex, although neuregulins.