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

Inclusion Criteria: * Has LS-SCLC (stage I-III, by American Joint Committee on Cancer \[AJCC\] 8th Edition Cancer Staging) and no evidence of extensive stage disease. Participants may enroll at any time between diagnosis and initiation of definitive concurrent chemoradiation or surgery followed by adjuvant chemotherapy. Correlative analyses collected during standard of care definitive concurrent chemoradiation or surgery followed by adjuvant chemotherapy are mandatory * Male/female participants who are at least 18 years of age on the day of signing informed consent with histologically confirmed diagnosis of small cell lung cancer or high grade neuroendocrine carcinoma will be enrolled in this study * Contraception requirements should conform with Clinical Trials Facilitation and Coordination Group (CTFG) guidelines. The pembrolizumab standard for use of highly effective contraceptive methods for persons of child-bearing potential (POCBP) is 120 days (5 half-lives) after the last dose. Please either list the contraception requirement for each compound in the study or use the longest time frame that covers requirements for all compounds in the study * Similarly, Company standard for abstaining from breastfeeding after study intervention is at least 5 half-lives. For pembrolizumab, this is 120 days * No radiological imaging evidence of disease progression after completion of definitive concurrent chemoradiation or surgery followed by adjuvant chemotherapy * The participant (or …