This is a single-arm, single-center, exploratory clinical study conducted at Shanghai Pulmonary Hospital, Tongji University. The study evaluates the effectiveness and safety of first-line treatment with benmelstobart (an immunotherapy), anlotinib (an anti-angiogenic drug), platinum-etoposide chemotherapy, and concurrent thoracic radiotherapy in participants with previously untreated, unresectable limited-stage small cell lung cancer (LS-SCLC).

Eligible participants are aged 18 to 75 years, with histologically or cytologically confirmed limited-stage SCLC (VALG staging), no prior systemic treatment for lung cancer, measurable lesions by RECIST 1.1, ECOG performance status 0-1, and adequate organ function.

Participants receive 4 cycles of induction therapy (21 days per cycle), including benmelstobart intravenously every 3 weeks, anlotinib orally for 2 weeks on / 1 week off, and chemotherapy with carboplatin or cisplatin plus etoposide. Thoracic radiotherapy (60-70 Gy in 30-35 fractions) is given concurrently with chemotherapy cycles 1-3. After induction, participants receive maintenance therapy with benmelstobart plus anlotinib for up to 2 years or until disease progression or unacceptable side effects.

The primary objective is to assess the Objective Response Rate (ORR) as evaluated by investigators using RECIST 1.1. Secondary objectives include progression-free survival (PFS), overall survival (OS), disease control rate (DCR), duration of response (DOR), and safety assessments of adverse events graded by CTCAE 5.0.

A total of 27 participants will be enrolled. The study is expected to start in March 2026, complete enrollment by September 2027, and end in March 2029. All participants will be regularly followed for efficacy and safety.

Inclusion Criteria:

• 1: Histologically or cytologically confirmed inoperable limited-stage small cell lung cancer (LS-SCLC) (per VALG staging).

  2: No prior systemic therapy for limited-stage small cell lung cancer

  3: Presence of measurable lesions as defined by RECIST 1.1. A previously irradiated lesion may be considered measurable only if it has demonstrated clear progression after radiotherapy and is not the sole lesion

  4: Age ≥ 18 and ≤ 75 years

  5: ECOG performance status: 0-1

  6: Expected survival ≥ 3 months

  7: Adequate hematologic and organ function, defined as meeting the following criteria: a) Hematologic function (no transfusion of blood or blood products, no G-CSF or other hematopoietic growth factors within 14 days): i. Absolute neutrophil count (ANC) ≥ 1.5 × 10⁹/L (1,500/mm³); ii. Platelet count (PLT) ≥ 100 × 10⁹/L (100,000/mm³); iii. Hemoglobin (HB) ≥ 80 g/L. b) Renal function: i. Calculated creatinine clearance (CrCl) ≥ 50 mL/min; ii. Urine protein < 2+ or 24-hour urine protein quantification < 1.0 g. c) Hepatic function: i. Serum total bilirubin (TBil) ≤ 1.5 × ULN; ii. AST and ALT ≤ 2.5 × ULN; iii. Serum albumin (ALB) ≥ 28 g/L. d) Coagulation function: i. International normalized ratio (INR) and activated partial thromboplastin time (APTT) ≤ 1.5 × ULN. e) Cardiac function: i. Left ventricular ejection fraction (LVEF) ≥ 50%.

  8: Subjects voluntarily participate in this study, provide written informed consent, demonstrate good compliance, and agree to comply with follow-up procedures.

Exclusion Criteria:

• 1: Prior use of anti-angiogenic agents such as anlotinib, apatinib, bevacizumab, or related immunotherapeutic agents targeting PD-1, PD-L1, etc

  2: Presence of multiple factors affecting oral medication absorption (e.g., inability to swallow, status post gastrointestinal resection, chronic diarrhea, intestinal obstruction, etc.).

  3: Uncontrolled pleural effusion, pericardial effusion, or ascites requiring repeated drainage.

  4: Patients with imaging evidence of tumor invasion adjacent to major blood vessels, or judged by the investigator to have a high risk of fatal massive hemorrhage due to tumor invasion of major blood vessels during the subsequent study period.

  5: History of severe bleeding tendency or coagulopathy, including but not limited to: clinically significant hemoptysis (more than one tablespoon per day) within 3 months prior to enrollment; or clinically significant bleeding symptoms or bleeding diathesis within 4 weeks prior to randomization, such as gastrointestinal bleeding, hemorrhagic gastric ulcer (including gastrointestinal perforation and/or fistula; however, patients with surgically repaired gastrointestinal perforation or fistula may be eligible), unhealed wounds, ulcers, or fractures, etc.

  6: Undergoing major surgical treatment, incisional biopsy, or significant traumatic injury within 28 days prior to randomization.

  7: History of arterial/venous thrombotic events within 6 months prior to randomization, such as cerebrovascular accident (including transient ischemic attack), deep vein thrombosis, and pulmonary embolism.

  8: Development of active autoimmune disease requiring systemic therapy (e.g., disease-modifying agents, corticosteroids, or immunosuppressants) within 2 years prior to the first dose.

  9: Any other conditions that, in the judgment of the investigator, would render the patient ineligible for study enrollment.

The decision to share individual participant data (IPD) is currently undecided. This is an exploratory single-center clinical study, and IPD sharing will be re-evaluated after study completion and primary results analysis. Factors to be considered include the protection of participant privacy, compliance with ethical committee requirements, and the scientific validity of secondary research using the shared data. If IPD sharing is approved in the future, access will be provided in accordance with ClinicalTrials.gov guidelines and relevant regulatory requirements.