• All subjects voluntarily participated in the study and signed informed consent;

• Male or female aged ≥18 years and ≤75 years;

• Expected survival time ≥3 months;

• ECOG 0-1;

• Patients with extensive-stage small-cell Lung cancer confirmed by histopathology and/or cytology (according to Veterans Administration Lung Study Group (VALG) staging);

∙ Cohort\_A cohort of patients with extensive-stage small cell lung cancer who had failed or were intolerant to 3 or more lines of systemic antitumor therapy. The so-called intolerance refers to the patients who have received standard treatment and have grade 3-4 adverse reactions, and the patients refuse to continue the original regimen.

‣ Cohort\_B Stage I subjects with previous failure or intolerance to standard therapy for extensive-stage small cell lung cancer;

‣ Cohort\_B Stage II patients who have not received any previous systemic anti-tumor therapy for extensive-stage small cell lung cancer;

• Consent to provide archival tumor tissue specimens (10 unstained sections (anti-slip) surgical specimens (thickness 4-5μm)) or fresh tissue samples from primary or metastatic lesions within 3 years. If participants cannot provide tumor tissue samples, they can be enrolled if they meet other inclusion and exclusion criteria, after the evaluation of the investigator;

• Must have at least one measurable lesion according to RECIST v1.1 definition; Lesions that had been previously treated with radiation could be included in a measurable lesion only if there was definite disease progression after radiation therapy.

• Organ function level must meet the following criteria:

∙ Blood routine: hemoglobin (HGB) ≥ 90g/L; Absolute neutrophil count (NEUT) ≥ 1.5×10 9 /L; Platelet count (PLT) ≥ 100×10 9 /L;

‣ Renal function: creatinine (Cr) ≤1.5 ULN, or creatinine clearance (Ccr) ≥50 mL/min (according to Cockcroft and Gault formula).

‣ Liver function: total bilirubin (TBIL≤1.5 ULN), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were all ≤2.5 ULN, and AST and ALT were both ≤5.0 ULN when liver metastasis was present;

‣ coagulation function: international normalized ratio (INR) ≤1.5 and activated partial thromboplastin time (APTT) ≤1.5ULN;

‣ no severe cardiac dysfunction with left ventricular ejection fraction ≥50%;

‣ proteinuria ≤2+ or ≤1000mg/24h;

• Toxicity of previous antineoplastic therapy has returned to ≤ grade 1 as defined by NCI-CTCAE v5.0 (except for asymptomatic laboratory abnormalities such as ALP elevation, hyperuricemia, and hyperglycemia, as judged by the investigator, and toxicity without safety risk, such as alopecia, grade 2 peripheral neurotoxicity, or decreased hemoglobin ≥90g/L, as judged by the investigator);

⁃ For premenopausal women with childbearing potential, a pregnancy test must be performed within 7 days before the start of treatment, the serum or urine pregnancy test must be negative, and the patient must not be lactating; All enrolled patients should take adequate barrier contraception during the whole treatment cycle and for 6 months after the end of treatment.