Study of Gemcitabine Maintenance Treatment in Patients With Extensive SCLC Patients

Inclusion Criteria: 1. ≥18 years 2. PS=0,1,2 3. Patients who were diagnosed by the histologic, cytologic diagnosis of extensive small cell lung cancer 4. Patients received Etoposide combined with platinum based first-line chemotherapy 6 cycles and there is evidence show the patent is PR/CR/SD 5. Expected lifetime\>12 weeks 6. Signed written informed consent Exclusion Criteria: Small cell lung cancer non small cell hybrid Women during pregnancy or lactation previously treated with two or more than two kinds of treatment Any non remission of \>CTCAE caused tumor treatment past grade 2 toxicity Ccr\<30 ml/min (calculated by Cockcroft-Gault formula) hepatic insufficiency： 1. Tbil\> 1.5×ULN 2. ALT and AST \> 2.5×ULN (Patients with liver metastasis\>5×ULN) Alkaline phosphatase\>2.5 ×ULN(Patients with liver metastasis\>5×ULN) 3. Severe symptomatic heart disease 4. Symptomatic brain metastases 5. In the last 5 years have been or are suffering from other histological types of malignant tumor 6. There are serious or uncontrolled systemic diseases 7. During the study period planned radiotherapy on target lesion 8. During the study period, plans to use other antineoplastic therapy 9. Clinical study on treatment of 30 days beginning period prior to participate in any study drug