Serplulimab Combined With CCRT for LS-SCLC.

This study tests whether adding serplulimab (an immunotherapy drug) to standard combined chemotherapy and radiation treatment improves outcomes for people with limited-stage small cell lung cancer — meaning the cancer is confined to one area of the chest. **You may be eligible if...** - You are 18 or older with a confirmed diagnosis of limited-stage small cell lung cancer (Stage II or III) - You have not had any prior chemotherapy, radiation, immunotherapy, or targeted therapy for this cancer - You are generally healthy and active (good performance status) - You have measurable cancer on scans - You are not pregnant or breastfeeding and are willing to use contraception during and for 6 months after treatment **You may NOT be eligible if...** - Your small cell lung cancer is extensive (spread widely beyond the chest) - You have had previous cancer treatment for small cell lung cancer - You have an active autoimmune disease requiring ongoing treatment - You have HIV, active hepatitis B or C, or active tuberculosis - You have received a live vaccine within 30 days before starting - You have a history of serious lung inflammation or pneumonia requiring steroids Talk to your doctor to see if this trial is right for you.