METHODS Three hundred and thirty patients with advanced NSCLC will be included to receive Paclitaxel 175 mg/m2 and Cisplatin 80 mg/m2 (PC) every 21 days for 6 cycles. Patients will be randomized to receive ATRA 45 mg2/day or placebo 1 week before treatment until completing six cycles. Imaging studies will be performed prior and after two cycles of CT to assess response. RAR beta and RAR alfa expression will be analyzed by immunohistochemistry in lung tumoral tissue and in the adjacent lung tissue.