Inclusion Criteria:
* The patient fully understands this study, voluntarily participates and signs an informed consent form (ICF).
* Age ≥ 18 years old;
* Patients with extensive stage small cell lung cancer diagnosed by pathology or histology;
* According to RECIST 1.1 standard, patients have at least one measurable target lesion; For lesions that have undergone radiation therapy in the past, they can only be included as measurable lesions if there is clear disease progression after radiation therapy;
* Progression confirmed by imaging examination after 6 months of first-line radiotherapy and chemotherapy containing platinum drugs or platinum regimen radiotherapy and chemotherapy ± immunotherapy;
* Eastern Cancer Collaborative Group (ECOG) physical fitness score: 0-2 points;
* Estimated survival time ≥ 3 months;
* Absolute neutrophil count (ANC) ≥ 1.5 x 10 \^ 9/L, platelet count ≥ 90 x 10 \^ 9/L, and hemoglobin count ≥ 90 g/L (no blood transfusion, blood products, use of granulocyte colony-stimulating factor or other hematopoietic stimulating factor correction within 14 days prior to laboratory examination);
* Liver and kidney function: serum creatinine ≤ 1.5 times the upper limit of normal value; AST and ALT ≤ 2.5 times the upper limit of normal values (≤ 5 times the upper limit of normal values for patients with liver invasion); Total bilirubin ≤ 1.5 times the upper limit of normal value (≤ 3 times the upper limit of normal value for patients with liver invasion);
* Women of childbearing age must undergo a pregnancy test (serum) within 7 days before enrollment, and the result is negative. They are willing to use appropriate methods of contraception during the trial period and 6 months after the last administration of the trial drug;
Exclusion Criteria:
* Patients with large cell neuroendocrine tumors and mixed small cell carcinoma;
* Patients with active brain metastasis or central nervous system invasion confirmed by imaging evaluation and/or biopsy (prednisone equivalent dose ≥ 10mg);
* There is an hypersensitivity reaction to any investigational drug or its components;
* Severe uncontrolled concurrent infections or other serious uncontrolled concomitant diseases, moderate or severe kidney injury; (such as progressive infection, uncontrollable hypertension, diabetes, etc.);
* Heart function and disease meet one of the following conditions:
1. Long QTc syndrome or QTc interval\>480 ms;
2. Complete left bundle branch block, II or III degree atrioventricular block;
3. Severe and uncontrolled arrhythmias that require medication treatment;
4. The New York College of Cardiology has a classification of ≥ III;
5. Cardiac ejection fraction (LVEF) below 50%;
6. A history of myocardial infarction, unstable angina, severe unstable ventricular arrhythmias, or any other arrhythmias requiring treatment, a history of clinically severe pericardial disease, or evidence of acute ischemic or active conduction system abnormalities on electrocardiogram within the 6 months prior to recruitment.
* Active infection of hepatitis B and hepatitis C (hepatitis B B virus surface antigen is positive and hepatitis B B virus DNA exceeds 1x103 copies/mL; hepatitis C virus RNA exceeds 1x103 copies/mL);
* Human Immunodeficiency Virus (HIV) infection (HIV antibody positive);
* Has previously or currently suffered from other malignant tumors (except for effectively controlled non melanoma skin basal cell carcinoma, breast/cervical carcinoma in situ, and other malignant tumors that have not been treated and have been effectively controlled within the past five years);
* Pregnant and lactating women, as well as patients of childbearing age who are unwilling to take contraceptive measures;
* Patients with other malignant tumors that require treatment; The researchers determined that patients who are not suitable to participate in this study.
