Lung cancer is a metastatic cancer whose cancer cells develop in the bronchi or alveoli and grow along the blood or lymphatic vessels. There are two types of lung cancer based on the size and shape of the cancer cell; non-small cell lung cancer (NSCLC) takes 75% and small cell lung cancer takes 25%. Lung cancer is usually difficult to find at an early stage and is diagnosed as lung cancer when it is already progressing. So the prognosis tends to be poor. Patients with EGFR mutation are known to show very high pharmacological responses to EGFR tyrosine kinase inhibitor (TKI) such as Gefitinib (Iressa, AstraZenca) and Erlotinib (Tarceba, Roche). We expect that genotyping the EGFR genes of lung cancer patients will allow prediction of drug response prior to treatment and this will lead to effective treatment of lung cancer.