This is a phase II study evaluating a new combination therapy for untreated extensive-stage small cell lung cancer. The treatment involves an initial phase with the drug Bemotuzumab plus standard chemotherapy and anlotinib, followed by a phase combining Bemotuzumab, anlotinib, and chest radiation. The primary objectives are to assess the efficacy of this approach in delaying cancer growth (progression-free survival) and to evaluate its safety in approximately 25 patients.

This is an exploratory Phase II clinical trial for previously untreated extensive-stage small cell lung cancer (ES-SCLC). The study evaluates a novel three-phase sequential treatment strategy: patients first receive induction therapy with Bemotuzumab combined with standard chemotherapy and Anlotinib; those achieving disease control then proceed to consolidation therapy with Bemotuzumab, Anlotinib, and concurrent thoracic radiotherapy; followed by a maintenance phase with Bemotuzumab plus Anlotinib. The primary objectives are to assess the regimen's efficacy in prolonging progression-free survival (PFS) and to observe its safety profile. The study plans to enroll approximately 25 patients.

**Inclusion Criteria:**

1. Histologically or cytologically confirmed extensive-stage small cell lung cancer (ES-SCLC) per VALG staging.

2. No prior systemic therapy for ES-SCLC.

3. At least one measurable lesion as defined by RECIST 1.1 criteria.

4. Age 18-75 years.

5. ECOG performance status of 0-2.

6. Life expectancy of ≥3 months.

7. Adequate hematologic and organ function:

   • Absolute neutrophil count (ANC) ≥ 1.5 × 10^9/L.
   • Platelet count ≥ 100 × 10^9/L.
   • Hemoglobin ≥ 80 g/L.
   • Creatinine clearance ≥ 50 mL/min.
   • Total bilirubin ≤ 1.5 × upper limit of normal (ULN).
   • AST and ALT ≤ 2.5 × ULN.
   • Albumin ≥ 28 g/L.
   • INR and APTT ≤ 1.5 × ULN.
   • Left ventricular ejection fraction (LVEF) ≥ 50%.

8. For females of childbearing potential: negative serum pregnancy test within 3 days prior to dosing and agreement to use highly effective contraception.

9. For males: agreement to use barrier contraception.

10. Willing and able to provide written informed consent and comply with study procedures.

**Exclusion Criteria:**

1. Symptomatic brain metastases. (Asymptomatic, treated, and stable brain metastases for ≥1 month without steroids are allowed).
2. Prior thoracic radiotherapy for SCLC.
3. Prior treatment with anti-angiogenic agents (e.g., anlotinib, bevacizumab) or anti-PD-1/PD-L1 therapies.
4. Factors affecting oral medication intake (e.g., inability to swallow, major gastrointestinal resection).
5. Uncontrolled effusions requiring repeated drainage (pleural, pericardial, or ascites).
6. Imaging evidence of tumor invasion of major blood vessels or high risk of fatal hemorrhage as judged by the investigator.
7. History of significant bleeding tendency or coagulopathy, including clinically significant hemoptysis (>1 tablespoon daily within 3 months) or significant bleeding within 4 weeks prior to enrollment.
8. Major surgical procedure, open biopsy, or significant traumatic injury within 28 days prior to enrollment.
9. Arterial/venous thrombotic events within 6 months prior to enrollment (e.g., cerebrovascular accident, deep vein thrombosis, pulmonary embolism).
10. Active autoimmune disease requiring systemic treatment within 2 years prior to first dose.
11. Any other condition that, in the investigator's judgment, increases risk or renders the patient unsuitable for the study.

De-identified individual participant data for all primary and secondary outcome measures will be made available.

Data will be available within 6 months of study completion

Data access requests will be reviewed by an external independent review panel. Requestors will be required to sign a Data Access Agreement.

This is an open-label study. No masking (blinding) is used.