Lung cancer, the most common cancer worldwide, remains the leading cause of cancer death. Approximately two-thirds of all patients with newly diagnosed non-small-cell lung cancer (NSCLC) present with advanced stage that palliative chemotherapy is the only appropriate measure. The standard treatment for this patient population consists of third generation platinum-based doublet regimen for no more than 6 cycles followed by watch and wait until disease progression (PD) before the administration of second-line and third-line systemic anticancer therapeutic agents. Patients who go on to receive second-line therapy represent a selected subgroup with an improved overall prognosis.

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.

Inclusion Criteria:

• Histologic or cytologic confirmed diagnosis of Stage IV NSCLC according to 2009 the seventh edition of TNM staging of lung tumors.
• No disease progression after four cycles of first-line chemotherapy with gemcitabine plus cisplatin (running period) within one month before the enrollment.
• Brain metastases are permitted if treated with full course of whole brain radiotherapy without the presence of symptomatic central nervous system metastases.
• ECOG score 0-1

Exclusion Criteria:

• First-line chemotherapy other than combination treatment of gemcitabine plus cisplatin
• Other therapy including targeted therapy, immunotherapy and prior radiotherapy for the treatment of the primary tumor prior to enrollment.
• Active infection
• Inadequate liver and renal function.
• Serious concomitant systemic disorder incompatible with the study.
• Second primary malignancy (except in situ carcinoma of the cervix, adequately treated basal cell carcinoma of the skin, T1 vocal cord cancer in remission, or prior malignancy treated more than 5 years prior enrollment without recurrence)
• Presence of the pregnancy