Study of Sintlimab Maintenance Therapy in Patients With Extensive Small Cell Lung Cancer

Inclusion Criteria: * small cell lung cancer confirmed by pathology * extensive small cell lung cancer by imaging * at least one measurable lesion by RECIST 1.1 * ECOG 0-1 * adequate organ function * no other severe diseases conflicting with this regimen (such as autoimmune diseases, immunodeficiency, organ transplantation, etc) * no history of other maliganancies * Women of childbearing period must examinate for a negative pregnancy test within 7 days, use appropriate contraceptive measures during the study and 6 months after the trial. * agreement to participate in the study and signed informed consent from the patients Exclusion Criteria: * serious infectious diseases four weeks before enrollment * requirement intermittent use of bronchodilators or medical interventions; * the use of immunosuppressants before the enrollment, the amount of immunosuppressant used ≥10mg / day oral prednisone for more than 2 weeks; * severe allergies * severe mental disorders * abnormal coagulation function * previous or current pulmonary fibrosis, interstitial pneumonia, pneumoconiosis, radiation pneumonitis, severe lung damage, etc. * other situations considered by investigators not meet the inclusion criteria (including but not limited to symptomatic brain metastases)