Lung cancer is the leading cause of cancer death in Republic of Korea. After their initial diagnosis, only 10-20% of patients with advanced non-small cell lung cancer (NSCLC) survive for 5 years of longer. Given enormous advances in therapeutics such as novel targeted therapies and immunotherapies, survival rates are improving for advanced patients with NSCLC; 5-year survival rates range from 15% to 50%, contingent upon the biomarker. Detection of the specific molecular alteration as biomarker is thus crucial for identifying subgroups of NSCLC that contain therpapeutically targetable oncogenic drivers. This review examines the process of diagnosing lung adenocarcinoma with dominant biomarkers in order to customize treatment with appropriate targeted therapy.