EGF Receptor (EGFR, ErbB1) is a transmembrane protein that exerts tyrosine kinase activity upon ligand induced activation. EGFR can be activated by binding EGF or at least six other structurally related protein ligands, including TGFα, HBEGF, Betacellulin (BTC), Amphiregulin, Epiregulin, and Epigen. Upon activation, EGFR initiates a signaling cascade which includes dimerization and internalization, tyrosine phosphorylation, DNA synthesis of target genes, and, ultimately, cell proliferation. EGFR signaling plays a role in the growth and differentiation of normal cells, but elevated EGFR activity is correlated with the development and pathogenesis of certain cancers. Recombinant soluble human EGFR is a 621 amino acid glycoprotein compri