This study is a prospective, single-arm, multicenter, exploratory clinical trial. It aims to evaluate the efficacy and safety of tislelizumab combined with nintedanib as consolidation therapy for patients with limited-stage small cell lung cancer after concurrent chemoradiotherapy, and to explore the prognostic markers related to the therapeutic effect.

Inclusion Criteria:

1. Have a thorough understanding of this study and have voluntarily signed the informed consent form;
2. Age ≥ 18 years old, gender not restricted;
3. ECOG score 0-1;
4. Histologically or cytologically confirmed as limited-stage small cell lung cancer;
5. At least one measurable lesion (according to RECISTv1.1 criteria);
6. Expected survival ≥ 3 months;
7. Prophylactic cranial radiotherapy is permitted before consolidation therapy;
8. Adequate organ function reserve. The subjects must meet the following laboratory indicators: Before the sample collection during the screening period, the patient has not received blood transfusion or growth factor support treatment for ≤ 14 days and: absolute neutrophil count (ANC) ≥ 1.5 × 109/L, platelets ≥ 100 × 109/L, hemoglobin ≥ 90 g/L，Calculated creatinine clearance rate (CrCl) (Cockcroft-Gault formula): creatinine clearance rate ≥ 60 mL/min，Serum total bilirubin ≤ 1.5 × upper limit of normal (ULN) (total bilirubin of Gilbert's syndrome patients must be < 3 × ULN)，AST and ALT ≤ 2.5 × ULN，Patients not receiving anticoagulation treatment: international normalized ratio or activated partial thromboplastin time ≤ 1.5 × ULN，Albumin ≥ 25 g/L (2.5 g/dL).
9. Willing and able to comply with the study plan's visits, treatment plan, laboratory tests and other research procedures;
10. Pregnant women must undergo a serum pregnancy test 3 days before the first medication administration and the result must be negative. For pregnant women subjects and male subjects whose partners are pregnant women, they must agree to use effective contraceptive methods during the study and within 120 days after the last administration of the study drug.

Exclusion Criteria:

1. There are patients with lung metastasis from other primary malignant tumors.
2. Patients who have previously or concurrently had other systemic malignant tumors (excluding skin basal cell carcinoma, skin squamous cell carcinoma, and/or in situ cancer that has undergone radical resection), excluding those with cured skin basal cell carcinoma, skin squamous cell carcinoma, and/or in situ cancer that has undergone radical resection.
3. Patients who have previously received other systemic treatments for the current lung cancer, including chemotherapy, immunotherapy, targeted therapy, or anti-angiogenic therapy, other than induction radiotherapy and chemotherapy.
4. Patients who received other approved systemic immunomodulators (including but not limited to interferon, interleukin-2, tumor necrosis factor, thymus pentapeptide, and thymalfasin) within 4 weeks prior to the first administration.
5. Patients whose blood pressure control is not satisfactory after drug treatment (systolic blood pressure ≥ 160 mmHg, diastolic blood pressure ≥ 100 mmHg).
6. Patients with factors that significantly affect the absorption of oral medications, such as inability to swallow, chronic diarrhea, and intestinal obstruction, etc.
7. The investigator judges that the possibility of tumor invasion of important blood vessels and fatal bleeding caused by the tumor is relatively high during the treatment process.
8. Within 3 months before the study, there was significant clinical hemoptysis (more than 50 ml of hemoptysis per day), or there were significant clinical bleeding symptoms or obvious bleeding tendencies (such as gastrointestinal bleeding, gastric ulcer bleeding, gastrointestinal bleeding, hemorrhagic gastric ulcer, fecal occult blood ++ and above baseline, or having vasculitis, etc.)
9. Within 14 days before the first administration of the study drug, any traditional Chinese medicine used for controlling cancer was used.
10. Within 30 days before the first administration, the patient received live vaccines. Including but not limited to the following: mumps, rubella, measles, chickenpox/zoster (chickenpox), yellow fever, rabies, BCG (bacillus Calmette-Guérin), and typhoid vaccine (inactivated virus vaccine is allowed); or it is expected that the patient will need to receive live vaccines or attenuated live vaccines during the study period or within 5 months after the last administration
11. Within 14 days before the first administration of the study drug, any situation where systemic treatment with corticosteroids (prednisone or equivalent drugs > 10 mg/day) or other immunosuppressive drugs is required, and the investigator assesses that it has an impact on the study treatment
12. Patients with systemic autoimmune diseases that require systemic treatment, and the investigator assesses that it has an impact on the study treatment
13. Patients with interstitial lung disease, non-infectious pneumonia, or other uncontrolled diseases, including diabetes, pulmonary fibrosis, acute lung disease, etc., and the investigator assesses that it has an impact on the study treatment
14. Patients with a significant history of major diseases or clinical manifestations that may affect the function of organ systems, and the investigator assesses that it has an impact on the study treatment.
15. Within 14 days before the first administration of the study drug, severe chronic or active infections (including tuberculosis infection, etc.) that require systemic antibacterial, antifungal, or antiviral treatment (including HBsAg positive in the screening period and HBV-DNA detection value higher than the upper limit of the laboratory test department of the research center; (for subjects who tested HBV-DNA content < 500 IU/mL within 28 days before enrollment and have received at least 14 days of local standard antiviral treatment and are willing to continue antiviral treatment during the study period, they can be enrolled); active hepatitis C (defined as HBsAb positive in the screening period and HCV-RNA positive) subjects.
16. Uncontrolled active hepatitis B (defined as HBsAg positive in the screening period and HBV-DNA detection value higher than the upper limit of the laboratory test department of the research center; (for subjects who tested HBV-DNA content < 500 IU/mL within 28 days before enrollment and have received at least 14 days of local standard antiviral treatment and are willing to continue antiviral treatment during the study period, they can be enrolled); active hepatitis C (defined as HBsAb positive in the screening period and HCV-RNA positive) subjects
17. Known human immunodeficiency virus (HIV) infection (known HIV antibody positive)
18. Grade III-IV congestive heart failure (New York Heart Association classification), poorly controlled and with clinically significant arrhythmias
19. Any occurrence of arterial thrombosis, embolism or ischemia within 6 months prior to the inclusion in the treatment, such as myocardial infarction, unstable angina pectoris, cerebrovascular accident or transient ischemic attack, etc.
20. Concurrent participation in another therapeutic clinical study, unless it is an observational (non-interventional) clinical study or during the follow-up period of an interventional study.
21. Medical history or disease evidence, abnormal treatment or laboratory test values that may interfere with the test results and prevent the subject from fully participating in the study, or other conditions that the investigator considers as other potential risks and unsuitable for inclusion in the study. The investigator considers that there are other potential risks that make participation in this study unsuitable.