Test Details: Lung Cancer is the leading cause of cancer death worldwide. Chemotherapy for non small cell lung carcinoma (NSCLC), accounting for 85% of lung cancer cases, remains marginally effective. Epidermal growth factor receptor (EGFR) tyrosine kinase (TK) inhibitor, gefitinib (Iressa), was approved in several countries for the treatment of NSCLC. Mutations in the EGFR gene correlate with clinical responsiveness to the TK inhibitor. About 90% of the mutations detected in EGFR are composed either of in-frame deletion in exon 19 or a specific missense mutation in exon 21, with 5% mutation in exon 18. Screening for such mutation in lung cancer may identify patients responsive to gefitinib and erlotinib. In certain patients drug induced resistance is observed and is correlated with mutation in exon 20. A secondary point mutation that substitutes methionine for threonine at amino acid position 790 (T790M) produces a drug resistance to EGFR TK inhibitor.