Before 2009, nonsmall cell lung cancer (NSCLC) was one disease entity treated by cytotoxic chemotherapy that provided a response rate of 20-35 % and a median survival time (MST) of 10-12 months. In 2004, it was found that activated mutations of the epidermal growth factor receptor (EGFR) gene were present in a subset of NSCLC and that tumors with EGFR mutations were highly sensitive to EGFR tyrosine kinase inhibitors (TKI). Four phase III studies (North East Japan (NEJ) 002, West Japan Thoracic Oncology Group (WJTOG) 3405, OPTIMAL, and EUROTAC) prospectively compared TKI (gefitinib or erlotinib) with cytotoxic chemotherapy as first-line therapy in EGFR-mutated NSCLC. These studies confirmed that progression-free survival (PFS) with TKIs (as the primary endpoint) was significantly longer than that with standard chemotherapy (hazard ratio [HR] = 0.16-0.49) from 2009 to 2011. Although the NEJ 002 study showed identical overall survival (OS) between the arms (HR = 0.89), quality of life (QoL) was maintained much longer in patients treated with gefitinib. In conclusion, TKI should be considered as the standard first-line therapy in advanced EGFR-mutated NSCLC. Since 2009, a new step has been introduced in the treatment algorithm for advanced NSCLC.