Phase 3 Study of Toripalimab Alone or in Combination With Tifcemalimab as Consolidation Therapy in Patients With Limited-stage Small Cell Lung Cancer (LS-SCLC)

Inclusion Criteria:

Patients must meet all of the following inclusion criteria to be enrolled:

1. Male or female with age ≥ 18 years old at the time of informed consent.

2. Histologically or cytologically confirmed LS-SCLC using the Veteran's AdministrationLung Study Arm (VALSG) staging criteria (Appendix 3). Patients with TNM Stage I orII disease per AJCC 8th edition must be medically inoperable (as determined by theInvestigator) or the patient must refuse surgery.

3. Received CRT defined as: (1) 4 cycles of chemotherapy consisting of carboplatin orcisplatin and intravenously administered etoposide; (2) a total radiation dose of 60-66 Gy for the standard once daily (QD) radiotherapy regimen or 45 Gy for thehyperfractionated twice daily (BID) radiotherapy regimen; (3) Patients must begininvestigational interventions within 42 days of the last dose of chemotherapy.

4. Patients must have achieved a complete response (CR), partial response (PR), orstable disease (SD) after receiving curative platinum-based CRT and must not havedeveloped progressive disease (PD) prior to study entry.

5. Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0-1 .

6. Adequate organ function

7. Female patients of childbearing potential and male patients whose partners are womenof childbearing age.

8. Voluntarily agree to participate in the study, sign the informed consent form, andagree to comply with all study and follow-up procedures.

Exclusion Criteria:

Patients will be excluded from the study if they meet any of the following criteria.

1. Mixed SCLC and non-small cell lung cancer (NSCLC).

2. Received sequential chemoradiotherapy for LS-SCLC.

3. Failure to recover from toxicity of prior anticancer therapy to Common TerminologyCriteria for Adverse Events (CTCAE) Grade ≤ 1 (except alopecia) or levels specifiedin the inclusion/exclusion criteria, whichever is more severe.

4. Patients with active autoimmune disease, history of autoimmune disease.

5. History of immunodeficiency, including HIV seropositivity, other acquired congenitalimmunodeficiency diseases, or a history of organ transplantation or allogeneic bonemarrow transplantation.

6. History of confirmed or suspected interstitial lung disease or pneumonitis (exceptfor Grade 1 radiation pneumonitis not treated with corticosteroids).

7. The presence of active hepatitis B (HBV DNA ≥ 500 IU/mL), hepatitis C (hepatitis Cantibodies positive and HCV-RNA higher than the lower limit of detection of theanalytical method).

8. Any other malignancy diagnosed prior to the first dose of investigationalintervention, except those with a low risk for the development of metastases (5-yearsurvival rate > 90%), such as adequately treated basal cell or squamous cell skincancer, carcinoma in situ of the cervix or breast, or adequately treated localizedprostate cancer.

9. Women who are pregnant or breastfeeding.