Therapeutic implication of EGFR in lung cancer

Lung cancer is very frequent and associated with a high mortality. In the last 25 years therapeutic progress have been limited and do not allow a 5 year global survival rate exceeding to 13-14%. Tumor biology permits a better comprehension of cancerization mechanisms and offers hope of new treatments with targeted therapies which would he specific of cancer cells and so more efficient and less toxic. Epidermal growth factor (EGF) pathway and its receptor (EGFR) expressed by most lung cancer cells is the most successfully completed example. The bond of EGF with its receptor stimulates tyrosine kinase domain of EGFR and allows transduction of an activating signal Inhibition of this signaling pathway stops tumor growth. Several agents are in development, from preclinical studies to phase III trials. It is a matter of humanized monoclonal antibodies, such as C225 (cetuximab), targeted against EGFR, or small molecules inhibiting tyrosine ;kinase activity of EGFR including ZD1839 (Iressa(R)), OSI774 (Tarceva(R)) or CI1033, and last antisense oligonucleotides. Antibodies and small molecules are well tolerated and are responsible for limited amount of side effects, mostly cutaneous toxicity and diarrhoea. Antitumor activity has been observed in monotherapy reaching up to 25% of clinical responses in the best series. EGFR inhibition seems to be also promising in combination with chemotherapy according to the synergy observed in preclinical studies and response rate up to 50% have been reported. But phase III studies have been disappointing and additional studies are warranted before consideration for a current daily practice, mostly that severe secondary effects were reported with pulmonary toxicities. In particular it remains to explain why clinical responses do not appear correlated with EGFR expression.