The main purpose of tumor classification is to distinguish clear differences such as deciding treatment or showing a peculiar characteristic. In the treatment of lung cancer, the standard for treatment selection is to make the important classification of small cell lung cancer(SCLC)and non-small cell lung cancer(NSCLC). This is based on the fact that with a clinical-pathology difference and treatment reactivity, the prognosis differs between SCLC and NSCLC. In the 21st century, it has become insufficient to choose a treatment only by the classification of NSCLC with the advent of gefitinib a molecular target drug. Thus, treatment must be chosen in terms of the presence or absence of adenocarcinoma, an ethnic group, gender, a smoking history, and also the gene mutation. Moreover, it was reported by ASCO in 2008 that efficacy of pemetrexed is low for non-squamous cell carcinoma. From now on, not the NSCLC classification, but further detailed classification is needed to choose a treatment. Treatment selection in terms of the individual will be possible with ongoing study.