⁃ The subjects voluntarily joined the study, signed the informed consent, and had good compliance;

⁃ 18 years old ≤age≤ 75 years old (calculated on the date of signing the informed consent);

⁃ Eastern Cooperative Oncology Group (ECOG) score 0 \

• 1;

⁃ Expected survival greater than 12 weeks.

⁃ Histologically or cytologically confirmed Extensive stage small cell lung cancer (ES-SCLC) (according to the Veterans Administration Lung Cancer Society (VALG) disease staging system).

⁃ had not received systemic therapy for ES-SCLC (including systemic chemotherapy, molecular targeted drug therapy, biological therapy and other investigational therapeutic drugs, etc.) or immune checkpoint inhibitor therapy.

⁃ Patients receiving chemoradiotherapy for previously limited-stage SCLC must be treated for cure, and there must be a treatment-free interval of at least 6 months from the last course of chemotherapy, radiotherapy, or chemoradiotherapy to the diagnosis of extensive SCLC.

⁃ Confirmed presence of at least one measurable lesion according to RECIST 1.1 criteria. Note: Measurable target lesions cannot be selected from previous radiotherapy sites. If the target lesion of the previous radiotherapy site is the only alternative target lesion, the investigator should provide pre - and post-imaging data showing significant progression of the lesion.

⁃ Laboratory inspection meets the following standards:

∙ Hemoglobin (HGB) ≥ 90g/L;

‣ Neutrophil absolute value (NEUT) ≥ 1.5× 10 9 /L;

‣ Platelet count (PLT) ≥ 90× 10 9 /L;

‣ Total bilirubin (TBIL) ≤ 1.5 times the upper limit of normal value (ULN);

‣ Alanine transferase (ALT) and aspartate transferase (AST) ≤ 2.5×ULN. ALT and AST≤ 5×ULN if accompanied by liver metastasis;

‣ Serum creatinine (CR) ≤ 1.5×ULN or creatinine clearance (CCR) ≥60 mL /min;

‣ Prothrombin time (PT), activated partial thromboplastin time (APTT), International standardized ratio (INR) ≤ 1.5×ULN (no anticoagulant therapy).

⁃ Women of reproductive age should agree that effective contraception must be used during the study period and for 6 months after the end of the study, and that serum or urine pregnancy tests are negative within 7 days prior to study enrollment; Men should agree that effective birth control must be used during the study period and for 6 months after the end of the study period.