EGFR (epidermal growth factor receptor) exists on the cell surface and is activated by the binding of its specific ligands, including epidermal growth factor and transforming growth factor α. EGFR dimerization stimulates its intrinsic intracellular protein-tyrosine kinase activity. As a result, autophosphorylation of several tyrosine (Y) residues on the C-terminal domain of EGFR occurs. These include Y992, Y1045, Y1068, Y1148 and Y1173. This autophosphorylation elicits downstream activation and signaling by several other proteins that associate with the phosphorylated tyrosines through their own phosphotyrosine-binding SH2 domains. These downstream signaling proteins initiate several signal transduction cascades, principally the MAPK, Akt and JNK pathways, which lead to DNA synthesis and cell proliferation. Such proteins modulate phenotypes such as cell migration, adhesion, and proliferation. Activation of the receptor is important for the innate immune response in human skin.

Many therapeutic approaches are aimed at EGFR. The monoclonal antibodies block the extracellular ligand binding domain. With the binding site blocked, signal molecules can no longer attach and activate the tyrosine kinase. Another therapeutic method involves using small molecules to inhibit the EGFR tyrosine kinase on the cytoplasmic side of the receptor. Without kinase activity, EGFR is unable to activate itself, which is a prerequisite for the binding of downstream adaptor proteins. Ostensibly by halting the signaling cascade in cells that rely on this pathway for growth, tumor proliferation and migration is diminished

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