Inclusion Criteria:
1. Subject volunteered to participate in the study and signed an informed consent;
2. Male or female aged ≥18 years and ≤75 years;
3. Expected survival time ≥3 months;
4. ECOG score 0-1;
5. Newly diagnosed patients with extensive-stage small cell lung cancer confirmed by histopathology and / or cytology;
6. A archived tumor tissue sample or fresh tissue sample of the primary or metastatic lesion must be provided within 3 years;
7. At least one measurable lesion meeting the RECIST v1.1 definition was required;
8. No blood transfusion and no use of cell growth factors and/or platelet-raising drugs within 14 days before screening, and the organ function level must meet the requirements;
9. The toxicity of previous antineoplastic therapy has returned to ≤ grade 1 as defined by NCI-CTCAE v5.0;
10. For premenopausal women of childbearing potential, a pregnancy test must be performed within 7 days before the initiation of treatment, a 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 entire treatment cycle and for 6 months after the end of treatment.
Exclusion Criteria:
1. Prior use of ADC drug therapy with small molecule toxins as topoisomerase I inhibitors;
2. Prior treatment with any systemic anti-tumor regimen for extensive-stage small cell lung cancer;
3. Pathology suggested small cell carcinoma containing non-small cell carcinoma components;
4. Subjects had used immunomodulatory drugs within 14 days before the first use of the study drug ;
5. Screening the history of severe cardiovascular and cerebrovascular diseases in the first half of the year ;
6. QT interval prolongation, complete left bundle branch block, III degree atrioventricular block, frequent and uncontrollable arrhythmia ;
7. Active autoimmune diseases and inflammatory diseases ;
8. Receiving long-term systemic corticosteroid therapy or equivalent anti-inflammatory active drugs or any form of immunosuppressive therapy prior to the first dose;
9. Other malignancies that have progressed or require treatment within 5 years prior to the first dose;
10. Have ILD requiring steroid therapy, or currently have ILD, or suspected ILD at screening;
11. Prior to initiation of study treatment, there were: a) poorly controlled diabetes mellitus; b) with severe complications of diabetes; c) glycosylated hemoglobin levels of 8% or more; d) hypertension that is poorly controlled by two antihypertensive drugs; e) history of hypertensive crisis or hypertensive encephalopathy;
12. Unstable thrombotic events requiring therapeutic intervention within 6 months prior to screening; Except for infusion set-related thrombosis;
13. Concurrent pulmonary disease leading to severe clinical impairment of respiratory function;
14. Patients with active central nervous system metastases;
15. Patients with large serosal effusions, or symptomatic serosal effusions, or poorly controlled serosal effusions;
16. History of allergy to recombinant humanized antibody or human-mouse chimeric antibody or to any excipient component of the experimental drug;
17. Prior organ transplantation or allogeneic hematopoietic stem cell transplantation;
18. Positive human immunodeficiency virus antibody, active tuberculosis, active hepatitis B virus infection, or active hepatitis C virus infection;
19. Severe infection within 4 weeks prior to first dose of study drug; Lung infection or active lung inflammation within 4 weeks;
20. Have participated in another clinical trial within 4 weeks prior to the first dose;
21. Have a history of psychotropic substance abuse and cannot be abstained from or have a history of severe neurological or psychiatric disorders;
22. Imaging examination showed that the tumor had invaded or encapsulated the large blood vessels in the chest;
23. Severe and non-healing wounds, ulcers, or fractures within 4 weeks prior to signing the informed policy;
24. Clinically significant bleeding or obvious bleeding tendency within 4 weeks prior to signing the informed policy;
25. Subjects who are scheduled to receive or receive a live vaccine within 28 days prior to the first dose;
26. Other conditions that the investigator considers unsuitable to participate in this clinical trial.
