Pembrolizumab After Radiation Therapy and Chemotherapy in Limited Stage Small Cell Lung Cancer

PRIMARY OBJECTIVE: I. To investigate progression free survival per Response Evaluation Criteria in Solid Tumors 1.1 (RECIST 1.1) as assessed by the investigator in patients with limited stage small cell lung cancer treated with adjuvant pembrolizumab. SECONDARY OBJECTIVES: I. Assess median overall survival compared to the historical control dataset (CONVERT trial1) median overall survival (OS) of 30 months. II. Assess the safety and tolerability of adjuvant pembrolizumab in patients with limited stage SCLC. EXPLORATORY/TRANSLATIONAL OBJECTIVES: I. To determine whether patients with detectable circulating tumor deoxyribonucleic acid (ctDNA) after curative intent therapy ("minimal residual disease \[MRD\] positive") experience shorter median progression free survival (PFS) compared to patients without detectable ctDNA after curative intent therapy ("MRD negative."). II. Determination of whether patients with ctDNA clearance at any point during curative intent therapy have superior median PFS compared to patients who do not experience ctDNA clearance during curative intent therapy. OUTLINE: Patients undergo radiation therapy and receive cisplatin or carboplatin on day 1 of each cycle and etoposide on days 1-3 for 4 cycles. Patients then receive pembrolizumab intravenously (IV) over 30 minutes on day 1 of each cycle. Cycles repeat every 21 days for 1 year in the absence of disease progression or unacceptable toxicity. Patients undergo positron emission tomography (PET) scan during screening. Patients also undergo magnetic resonance imaging (MRI) throughout the trial as well as computed tomography (CT). Additionally, patients undergo blood sample collection throughout the trial. After completion of study treatment, patients are followed up at 30 days, and every 12 weeks for 2 years.