Chemoimmunotherapy Plus Residual Lesion Irradiation for the Treatment of Extensive Stage Small-cell Lung Cancer

This study is testing whether people with extensive-stage small cell lung cancer (ES-SCLC) can benefit from targeted radiation to remaining tumor sites after responding to initial chemotherapy combined with immunotherapy (atezolizumab). Radiation may help destroy any remaining cancer cells that the drugs didn't fully eliminate. **You may be eligible if...** - You are 18 or older with a confirmed diagnosis of extensive-stage small cell lung cancer - Your disease has spread beyond one lung (e.g., other lung, pleura, or outside the chest) - You have measurable disease before starting platinum-based chemotherapy - Your physical performance is good (ECOG 0-1) - Your blood counts and organ function are within required ranges **You may NOT be eligible if...** - You have active autoimmune disease - You have had prior chest radiation to a degree that prevents safe re-treatment - You are pregnant or breastfeeding - You have uncontrolled brain metastases - You have had prior immunotherapy Talk to your doctor to see if this trial is right for you.