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

Prior treatment

• 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.
• Concomitant autoimmune disease, or long-term oral corticosteroid use (including oral corticosteroids within 14 days before treatment).
• 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).

Other illness

• Allergy to adebrelimab.
• 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.
• MRI evidence of leptomeningeal, brainstem, or spinal cord metastases, or symptomatic brain metastases (e.g., headache, nausea, vomiting, visual impairment, or visual field defects).
• Hypertension poorly controlled despite two antihypertensive agents (systolic blood pressure \>150 mmHg or diastolic blood pressure \>100 mmHg).
• Any deep vein thrombosis (allowed if stable on low-molecular-weight heparin or similar therapy for \>2 weeks), arterial thrombosis, or pulmonary embolism.

Lab values

• Poorly controlled blood glucose (defined as: 1. two consecutive fasting blood glucose values \>10 mmol/L; or 2. HbA1c ≥8%), or diabetic gangrene.

Other

• 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.
• 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.

• Age ≥18 years and ≤75 years.
• Histologically or cytologically confirmed SCLC.
• No prior thoracic radiotherapy or thoracic surgery.
• No prior systemic anti-tumor therapy.
• ECOG performance status 0-2 and life expectancy ≥12 weeks.
• At least one measurable lesion per RECIST 1.1.
• 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.
• 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.
• Urine protein ≤1+ or \<1000 mg/24h.
• All patients have provided full informed consent.