EGFR (epidermal growth factor receptor), also known as HER-1, ErbB1, or ErbB, is a transmembrane receptor tyrosine kinase that binds a subset of the EGF family ligands including EGF, Amphiregulin, TGF-alpha, Betacellulin, Epiregulin, HB-EGF, and Epigen. Ligand binding induces EGFR homodimerization as well as heterdimerization with ErbB2, resulting in kinase activation, tyrosine phosphorylation and cell signaling. EGFR can also be recruited to form heterodimers with the ligand-activated ErbB3 or ErbB4. EGFR signaling regulates multiple biological functions including cell proliferation, differentiation, motility, and apoptosis. EGFR is overexpressed in a wide variety of tumors and is the target of several anti-cancer drugs. Soluble receptors consisting of the extracellular ligand binding domain are generated by alternate splicing in human and mouse.