EGFR (Epidermal Growth Factor Receptor), also known as ERBB, mENA, ERBB1 and HER1, is the receptor for members of the EGF family and is a transmembrane glycoprotein that has tyrosine kinase activity. Receptor tyrosine kinase binding ligands of the EGF family and activating several signaling cascades to convert extracellular cues into appropriate cellular responses. Known ligands include EGF, TGFA/TGF-alpha, AREG, epigen/EPGN, BTC/betacellulin, epiregulin/EREG and HBEGF/heparin-binding EGF. Ligand binding triggers receptor homo and/or heterodimerization and autophosphorylation on key cytoplasmic residues. The phosphorylated receptor recruits adapter proteins like GRB2 which in turn activates complex downstream signaling cascades, including at least 4 major downstream signaling cascades: the RAS-RAF-MEK-ERK, PI3 kinase-AKT, PLCgamma-PKC and STATs modules, leading to cell proliferation. EGFR is widely recognized for its importance in cancer. Amplification and mutations of this gene have been shown to be driving events in many cancer types. Its role in non-small cell lung cancer, glioblastoma and basal-like breast cancers has spurred many research and drug development efforts.