EGFR and lung cancer: The present study was performed in EGFR-TKI-sensitive PC-9 (EGFR mutant/wild-type K-Ras) and EGFR-TKI-resistant A549 (wild-type EGFR/mutant K-Ras) human lung cancer cell lines to investigate the anti-proliferative effects of sorafinib as a single agent and in different schedules in combination with gemcitabine.