Review of epidermal growth factor receptor biology.

The epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein that constitutes one of four members of the erbB family of tyrosine kinase receptors. Binding of EGFR to its cognate ligands leads to autophosphorylation of receptor tyrosine kinase and subsequent activation of signal transduction pathways that are involved in regulating cellular proliferation, differentiation, and survival. Although present in normal cells, EGFR is overexpressed in a variety of tumor cell lines and has been associated with poor prognosis and decreased survival. EGFR activation also plays a role in resistance to chemotherapy and radiation treatment in tumor cells. Over the past two decades, much effort has been directed at developing anticancer agents that can interfere with EGFR activity. The most common pharmacologic approaches to inhibiting EGFR have been to develop monoclonal antibodies and small-molecule inhibitors. Monoclonal antibodies block ligand binding to the extracellular domain, whereas the small-molecule inhibitors exert their effects at the intracellular portion of the receptor to prevent tyrosine kinase phosphorylation and subsequent activation of signal transduction pathways. A number of EGFR inhibitors have been developed that can arrest tumor growth and, in some cases, cause tumor regression. When used in combination with cytotoxic treatments, chemotherapy, and radiation, EGFR inhibitors have been able to potentiate their anticancer activity.