Testing the Addition of Radiation Therapy to the Immune Therapy Treatment for ES-SCLC

This study tests whether adding targeted radiation therapy to an immunotherapy-based regimen improves long-term outcomes for people with extensive-stage small cell lung cancer (ES-SCLC) — the more advanced form of this aggressive type of lung cancer — after initial chemotherapy with serplulimab achieves disease control. **You may be eligible if...** - You are between 18 and 75 years old - You have been diagnosed with extensive-stage small cell lung cancer - You have already completed combination chemotherapy with serplulimab and your cancer responded (complete response, partial response, or stable disease) - You have not received prior systemic therapy for ES-SCLC - You have at least one measurable lesion and are in good general health (ECOG 0 or 1) **You may NOT be eligible if...** - Your cancer progressed during initial chemotherapy - You have uncontrolled brain metastases - You have serious heart, lung, or kidney problems - You have active autoimmune disease - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.