Switch maintenance therapy with pemetrexed or erlotinib in patients with advanced NSCLC without PD after first-line chemotherapy has been confirmed to improve progression free survival (PFS) and overall survival (OS) significantly compared with placebo in two large randomized controlled studies. However, continuation gemcitabine maintenance therapy in this setting yields conflicting results in the west, i.e.showing a prolongation of PFS without OS improvement. Thus, we investigate the efficacy and safety of continuation of gemcitabine maintenance therapy for patients with metastatic NSCLC with ECOG performance status of 0-1 and without PD after four cycles of first-line chemotherapy with gemcitabine and cisplatin in China.