EGF R (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 EGF R homodimerization as well as heterdimerization with ErbB2, resulting in kinase activation, tyrosine phosphorylation and cell signaling. EGF R can also be recruited to form heterodimers with the ligand-activated ErbB3 or ErbB4. EGF R signaling regulates multiple biological functions including cell proliferation, differentiation, motility, and apoptosis. EGF R 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.