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

This study is a multicenter, prospective investigation aiming to evaluate the efficacy and safety of low-dose radiotherapy (15Gy/1.5 Gy bid × 10 fractions) combined with 4-6 cycles of systemic chemotherapy concurrently with Adebrelimab, followed by Adebrelimab maintenance therapy for up to two years, in subjects with extensive-stage small cell lung cancer (ES-SCLC). Additionally, immunohistochemical detection of the expression levels of four key transcriptional proteins-YAP1, NEUROD1, ASCL1, and POU2F3-will be performed to guide the molecular subtyping of SCLC. Based on these findings, we will explore the differential therapeutic outcomes of this regimen across distinct molecular subtypes (A/N/P/Y/I/AN/QN), with the goal of identifying the subject population most likely to benefit from this treatment modality, thereby optimizing clinical decision-making.

Inclusion Criteria: 1. Age ≥18 years and ≤75 years; 2. Histologically or cytologically confirmed SCLC; 3. No malignant pleural effusion or pericardial effusion; 4. No prior history of thoracic radiotherapy or thoracic surgery; 5. No prior systemic anti-tumor therapy; 6. ECOG performance status 0-2, with a life expectancy of ≥12 weeks; 7. At least one measurable lesion per RECIST 1.1 criteria; 8. No history of interstitial pneumonia; 9. No history of immune-related pneumonitis; 10. No history of autoimmune diseases; 11. No history of significant active pulmonary infection; 12. No use of corticosteroid therapy within 14 days prior to enrollment; 13. No Grade ≥3 hematologic toxicity or hepatic/renal impairment; 14. No brainstem metastases and no significant neurological symptoms; 15. For subjects with coexisting HBV/HCV infection, hepatic impairment ≤ Grade 1 after prior active antiviral therapy; 16. All subjects have provided written informed consent; Exclusion Criteria: 1. Presence of interstitial pneumonia or infectious fever prior to treatment; 2. Comorbid autoimmune diseases or long-term oral corticosteroid use (including those who received oral corticosteroids within 14 days prior to treatment); 3. Prior history of thoracic radiotherapy or thoracic surgery; 4. Presence of Grade ≥3 hematologic toxicity or hepatic/renal impairment; 5. Hypersensitivity to adebrelimab; 6. Significant respiratory symptoms that preclude tolerance to radiotherapy; 7. Active hepatitis B or C infection, currently on antiviral therapy, and with liver function impairment of Grade 2 or above; 8. Presence of pleural effusion or pericardial effusion;