Epidermal growth factor receptor targeting in cancer.

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase of the ErbB family that is abnormally activated in many epithelial tumors. Several mechanisms lead to the receptor's aberrant activation that is observed in cancer, including receptor overexpression, mutation, ligand-dependent receptor dimerization, and ligand-independent activation. Two classes of anti-EGFR agents are currently approved for the treatment of patients with cancer: cetuximab, a monoclonal antibody directed at the extracellular domain of the receptor, and gefitinib and erlotinib, oral, low-molecular-weight (MW), adenosine triphosphate (ATP)-competitive inhibitors of the receptor's tyrosine kinase. Anti-EGFR monoclonal antibodies have demonstrated activity in the therapy of advanced colorectal carcinoma and in a variety of epithelial tumor types, including head and neck cancer and non-small cell lung cancer (NSCLC). The development of low MW, anti-EGFR tyrosine kinase inhibitors (TKIs) has been focused until recently on NSCLC, although responses have been reported for other types of cancer. Erlotinib was the only agent approved based on demonstrating improved survival, which was observed in patients with advanced NSCLC who previously had been treated with chemotherapy. Recent major advances in the EGFR field include the discovery of EGFR somatic mutations in NSCLC that have important implications for biology, treatment, clinical trial design, and methods for mutation detection. Clinical and survival benefits with anti-EGFR agents have been demonstrated in additional tumor types such as head and neck and pancreatic carcinomas. New agents with clinical activity are entering the clinic and new combinatorial approaches with anti-EGFR agents are being explored. Major efforts are, belatedly, attempting to identify molecular markers that can predict patients more likely to respond to anti-EGFR therapy.