Inhibition of the epidermal growth factor receptor in combined modality treatment for locally advanced non-small cell lung cancer.
Epidermal growth factor receptor 1 (EGFR 1 ) is a 170-kd glycoprotein that plays many roles in the growth of non-small cell lung cancer (NSCLC). There are four known receptors in the EGFR family. Binding of a ligand such as epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) causes EGFR to undergo a conformational change leading to autophosphorylation of EGFR and activation of the EGFR growth factor pathway. The protein products of the genes that are then expressed increase cell proliferation and angiogenesis and inhibit programmed cell death. EGFR is expressed in 40% to 80% of NSCLC. EGFR tyrosine kinase activity can be inhibited by antibody therapy, such as cetuximab, against the extracellular domain of EGFR or small-molecule therapy, such as gefitinib or erlotinib that blocks the adenosine triphosphate (ATP) binding site of the cytoplasmic domain. Both forms of EGFR inhibition have single-agent antitumor activity against previously treated NSCLC. Interestingly, EGFR expression does not correlate with response to EGFR inhibition therapy. Increased likelihood of responding to small-molecule therapy is associated with female gender, never smoking, adenocarcinoma, and acquired mutations of the EGFR ATP binding site in tumor cells. In previously treated NSCLC, the small-molecule erlotinib improved both quality of life and median survival as a single agent compared with best supportive care. Southwest Oncology Group 0023 is a large, phase III, randomized trial comparing concurrent chemoradiotherapy and consolidation docetaxel with or without maintenance small-molecule therapy with gefitinib. There is also strong preclinical evidence that EGFR inhibition is additive or synergistic with radiotherapy in NSCLC. In locally advanced head and neck cancer, the addition of cetuximab antibody therapy to radiation increased median survival from 28 to 54 months. Cancer and Leukemia Group B 30106 and a multi-institutional Australian phase I trial have shown that gefitinib can be added to concurrent chemoradiotherapy for stage III NSCLC without excessive toxicity. A phase I trial at the University of Chicago (Chicago, IL) has evaluated erlotinib with concurrent chemoradiotherapy in stage III NSCLC. Radiation Therapy Oncology Group 0324 is an on-going phase II trial studying cetuximab and concurrent chemoradiotherapy in stage III NSCLC.
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