[A simple view on lung cancer biology: The EGFR pathway]

Epidermal growth factor receptor (EGFR) is a cell membrane tyrosine kinase receptor. Activating mutations at exon 19 and 21 of the EGFR gene are associated with the occurrence and development of lung adenocarcinoma. These gain of function mutations predict responsiveness to EGFR tyrosine kinase inhibitors (TKis), erlotinib or gefitinib and are also a favorable prognostic factor in lung cancer. Sequencing is the recommended technique to detect the mutations, but other more sensitive technics are under evaluation. Treatment as first line therapy by gefitinib is limited to lung cancer patients harboring an EGFR mutation. Erlotinib can be given regardless of the EGFR status as second or third line therapy, as well as maintenance therapy in patients with a stable disease after platinum based chemotherapy. In EGFR mutated tumors, most patients present a recurrence of the disease, despite an initial response on EGFR TKis. Two mechanisms of secondary resistance have been identified, the selection of the T790M mutation in EGFR exon 20 and the MET amplification. Other molecular anomalies as the ras mutations or the EMLA-ALK protein fusion are mutually exclusive with the EGFR mutations and are associated with primary resistance to EGFR TKis.