Low-dose Thoracic Radiotherapy Followed by Adebrelimab Plus Chemotherapy, and Then Sequential Maintenance Therapy With Adebrelimab for Extensive-stage Small Cell Lung Cancer

Inclusion Criteria:

1. Age ≥18 years and ≤75 years.
2. Histologically or cytologically confirmed SCLC.
3. No prior thoracic radiotherapy or thoracic surgery.
4. No prior systemic anti-tumor therapy.
5. ECOG performance status 0-2 and life expectancy ≥12 weeks.
6. At least one measurable lesion per RECIST 1.1.
7. Adequate bone marrow function to tolerate anti-tumor therapy: WBC ≥3×10⁹/L, Hb ≥80 g/L, PLT ≥75×10⁹/L, and absolute neutrophil count (NEUT) ≥1.5×10⁹/L.
8. Essentially normal hepatic and renal function: 8.1. Serum creatinine ≤1.5×ULN or creatinine clearance (CrCl) ≥50 mL/min; 8.2. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤2.5×ULN (≤5×ULN is acceptable in patients with liver metastases); 8.3. Total bilirubin (TBIL) ≤1.5×ULN; 8.4. Albumin ≥30 g/L and prealbumin ≥150 g/L.
9. Urine protein ≤1+ or \<1000 mg/24h.
10. All patients have provided full informed consent.

Exclusion Criteria:

1. Pre-existing interstitial lung disease (with or without clinical symptoms) or uncontrolled infectious pneumonia (e.g., accompanied by cough, fever \>38°C, dyspnea, tachypnea, etc.) prior to treatment.
2. Concomitant autoimmune disease, or long-term oral corticosteroid use (including oral corticosteroids within 14 days before treatment).
3. Allergy to adebrelimab.
4. Positive HIV antibody, active hepatitis B (HBV-DNA \>10³ IU/mL), active hepatitis C (HCV-RNA above the lower limit of detection of the study site), active pulmonary tuberculosis (defined as: fever, night sweats, chest pain, etc.; or acid-fast bacilli found in sputum or bronchoalveolar lavage fluid; or chest CT showing active signs such as patchy infiltrates or cavities), or positive syphilis antibody.
5. Moderate or large pleural effusion (maximum depth \>3 cm on chest ultrasound or CT, estimated volume \>500 mL) or moderate or large pericardial effusion (maximum diastolic width \>1 cm on echocardiography, estimated volume \>100 mL), or poorly controlled pleural/pericardial effusion (defined as requiring ≥2 drainage procedures within 1 month). Patients may be enrolled if effusion becomes minimal or undetectable after drainage.
6. MRI evidence of leptomeningeal, brainstem, or spinal cord metastases, or symptomatic brain metastases (e.g., headache, nausea, vomiting, visual impairment, or visual field defects).
7. Severe cardiac or cerebrovascular disease, including: New York Heart Association (NYHA) class ≥2 heart failure; acute coronary syndrome (e.g., myocardial infarction, unstable angina) within 6 months before enrollment; frequent and uncontrolled arrhythmias (excluding transient atrial fibrillation/flutter) despite antiarrhythmic therapy for ≥2 weeks; acute cerebrovascular events (e.g., transient ischemic attack, cerebral infarction, cerebral hemorrhage).
8. Hypertension poorly controlled despite two antihypertensive agents (systolic blood pressure \>150 mmHg or diastolic blood pressure \>100 mmHg).
9. Poorly controlled blood glucose (defined as: 1. two consecutive fasting blood glucose values \>10 mmol/L; or 2. HbA1c ≥8%), or diabetic gangrene.
10. Any deep vein thrombosis (allowed if stable on low-molecular-weight heparin or similar therapy for \>2 weeks), arterial thrombosis, or pulmonary embolism.
11. Pregnant or lactating women, or women of childbearing potential who are unwilling to use effective contraception during the study and for at least 6 months after the last dose.