We analyzed clinical courses of Japanese patients of lung adenocarcinoma in order to assess the relation between each adverse event and efficacy of gefitinib, because gefitinib is one of the first-line treatments for advanced non-small cell lung cancer with EGFR mutation in guidelines of American Society of Clinical Oncology (ASCO) (Keedy et al. 2011) and the Japan Lung Cancer Society, and adenocarcinoma is the most common pathological type in lung cancer (Jemal et al. 2011). The gene discussed is EGFR; the disease is non-small cell lung carcinoma.