Inclusion Criteria:  Patients must be volunteered to participate in the clinical trial. Patients must sign the informed Consent form (ICF) and be willing to follow and be able to complete all test procedures.  Histologically or cytologically confirmed ES-SCLC (per the Veterans Administration Lung Study Group [VALG] staging system).  No patients with resectable or radical radiotherapy lung cancer. Patient must have no Epidermal Growth Factor Receptor (EGFR) mutation, Anaplastic lymphoma kinase (ALK) rearrangement, or ROS proto-oncogene 1 , receptor tyrosine kinase(ROS1) rearrangement.  Patient must be at least resistant to the first-line chemotherapy. Patients must have measurable disease based on Response Evaluation Criteria in Solid Tumors (RECIST) 1.1.  Patients can tolerate chemotherapy.  Exclusion Criteria:  Unclear diagnosis of SCLC. Resectable or radical radiotherapy SCLC. Contraindicated chemotherapy. Undergoing other active malignancies within 5 years or at the same time.Patients with localized curable tumors, such as basal cell carcinoma, squamous cell carcinoma, superficial bladder carcinoma, prostate carcinoma in situ, cervical carcinoma in situ, or breast carcinoma in situ, will not be excluded.  Positive test result for human immunodeficiency virus (HIV). Positive test result for active tuberculosis. Live vaccine was administered within 28 days of initial administration. Inactivated viral vaccines for seasonal influenza are allowed, except for live attenuated intranasal vaccines.  Pregnant or lactating women. A history of psychotropic substance abuse, drug abuse, or alcoholism. Other factors assessed by the sponsors.