Low-Dose Radiotherapy Plus Adebrelimab and Chemotherapy for Extensive-Stage Small Cell Lung Cancer

• 1.Patients with pathologically confirmed extensive-stage small cell lung cancer (ES-SCLC) according to VALG staging.
• 2. No prior systemic therapy for extensive-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 clear progression occurs after radiotherapy and this previously irradiated lesion is not the only lesion.
• 4. Aged 18-75 years.
• 5. ECOG performance status: 0-2.
• 6. Expected survival ≥3 months.

• 7. Adequate hematological and organ function, i.e., meeting the following criteria:

  a) Hematology (no blood transfusion or blood products and no use of G-CSF or other hematopoietic growth factors for correction within 14 days): i. Absolute neutrophil count (ANC) ≥1.5×10\^9/L (1,500/mm\^3); ii. Platelet count (PLT) ≥100×10\^9/L (100,000/mm\^3); iii. Hemoglobin (HB) ≥80 g/L. b) Renal: i. Calculated creatinine clearance (CrCl) ≥50 mL/min; ii. Urine protein \<2+ or 24-hour urine protein \<1.0 g. c) Hepatic: i. Serum total bilirubin (TBil) ≤1.5×ULN; ii. AST and ALT ≤2.5×ULN; iii. Serum albumin (ALB) ≥28 g/L. d) Coagulation: i. International normalized ratio (INR) and activated partial thromboplastin time (APTT) ≤1.5×ULN.

  e) Cardiac: i. Left ventricular ejection fraction (LVEF) ≥50%.

• 8. Female patients must meet one of the following conditions:

  1. Menopause (defined as no menstruation for at least 1 year and no other confirmed cause other than menopause); or
  2. Surgical sterilization (oophorectomy and/or hysterectomy); or
  3. Fertile but must meet:

  i. Serum pregnancy test within 3 days before drug administration must be negative; ii. Agree to use contraceptive measures with an annual failure rate \<1% (from signing the ICF until at least 6 months after the last dose of the study drug); iii. Must not breastfeed.

• 9. Male patients must take contraceptive measures as follows: when the partner is a woman of childbearing potential or the partner is pregnant, the male patient must remain abstinent or use a condom during the study treatment period and for at least 6 months after the last dose of the study drug to prevent embryonic exposure to the drug.
• 10. Participants voluntarily agree to participate in this study, sign the informed consent form (ICF), have good compliance, and are willing to cooperate with follow-up.

Exclusion Criteria:

• 1. Patients with symptomatic brain metastases. Patients may be enrolled if symptoms remain clinically stable for at least 1 month after treatment of brain metastasis lesions and no steroids or anticonvulsants have been used for at least 1 month before study entry.
• 2. Patients who have previously received thoracic radiotherapy for limited-stage SCLC.
• 3. Prior use of anti-angiogenic drugs such as anlotinib, apatinib, and bevacizumab, or related immunotherapy drugs targeting PD-1, PD-L1, etc.
• 4. Factors affecting oral medication (e.g., inability to swallow, post-gastrointestinal resection, chronic diarrhea, and intestinal obstruction, etc.).
• 5. Uncontrolled pleural effusion, pericardial effusion, or ascites requiring repeated drainage.
• 6. Imaging shows that the tumor has invaded the periphery of major blood vessels, or the investigator judges that during the subsequent study period the tumor is highly likely to invade major blood vessels and cause fatal massive bleeding.
• 7. History of severe bleeding tendency or coagulation dysfunction, including but not limited to: clinically significant hemoptysis within 3 months before enrollment (>1 tablespoon per day); or clinically significant bleeding symptoms or bleeding tendency within 4 weeks before grouping, such as gastrointestinal bleeding, bleeding gastric ulcer (including gastrointestinal perforation and/or fistula; however, patients with gastrointestinal perforation or fistula that has been surgically resected may be allowed to enroll), unhealed wounds, ulcers, or fractures, etc.
• 8. Major surgical treatment, incisional biopsy, or significant traumatic injury within 28 days before grouping.
• 9. Arterial/venous thrombotic events within 6 months before grouping, such as cerebrovascular accident (including transient ischemic attack), deep vein thrombosis, and pulmonary embolism.
• 10.Active autoimmune disease requiring systemic treatment (e.g., disease-modifying drugs, corticosteroids, or immunosuppressants) within 2 years before the first dose.
• 11.Other conditions that increase the risk of participating in the study or are related to the study drug and, according to the investigator's judgment, may make the patient unsuitable for inclusion in the study.