Lung cancer is a metastatic cancer which the cancer cells are developed in the bronchial tubes or alveoli and grow along the blood vessel or lymphatic vessel. There are two types of lung cancer based on the sizes and shape of the cancer cell; non-small cell lung cancer (NSCLC) takes 75% and small cell lung cancer takes 25%. Usually, it is hard to find lung cancer in the early stage and is diagnosed as lung cancer when it is already progressed. So the prognosis tends to be bad. It is known that the patients with EGFR mutation show very high drug responses against EGFR tyrosine kinase inhibitor (TKI) such as Gefitinib (Iressa, AstraZenca) and Erlotinib (Tarceba, Roche). We expect that genotyping EGFR genes of the lung cancer patients enables predicting drug response before treatment and this will lead effective lung cancer treatment.