This study investigates whether adding an investigational immunotherapy medication to the usual treatment can reduce the chance of small cell lung cancer growing or spreading. Small cell lung cancer is a type of cancer that starts in the lungs and can quickly spread to other parts of the body. The study involves participants receiving standard treatment, known as chemoradiation therapy, with or without the investigational medication.

Participants will be randomly assigned to one of two study arms. One arm will receive the standard chemoradiation therapy for up to 7 weeks, while the other arm will receive the same therapy plus the investigational medication for up to one year. All participants will be monitored for side effects during the treatment period. Additionally, doctors will conduct regular follow-ups to monitor the participants' health after the treatment.

• Who can participate: Individuals at least 18 years old with limited stage small cell lung cancer can participate. Those with previous surgical resection, prior invasive malignancy, metastatic disease, certain co-morbidities, organ transplant history, immunodeficiency, or who are pregnant are excluded.
• Study details: Participants will receive standard chemoradiation therapy, with or without an investigational immunotherapy medication. A placebo is not used.
• Study Timelines: The study will last one year.