Key Inclusion Criteria:  Patient has pathologically (histologically or cytologically) proven diagnosis of small cell lung cancer Has limited-stage disease (stage Tx, T1-T4, N0-3, M0; AJCC staging, 8th edition), and can be safely treated with definitive radiation doses. Patient has not received any prior treatment for LS-SCLC. Patient has measurable disease as assessed according to RECIST v1.1 that is appropriate for selection as a target lesion for repeat measurement, as determined by local site investigator/radiology review ECOG Performance Status ≤ 2 assessed within 7 days before the first administration of study intervention, and must have a life expectancy of ≥ 12 weeks.  Key Exclusion Criteria:  Mixed small cell lung cancer histology. Note: mixed SCLC with the component of neuroendocrine carcinoma origin is considered eligible Have received surgical resection for LS-SCLC Any patient for whom the tumor is considered resectable by surgery or stereotactic body radiation therapy/stereotactic ablative radiotherapy should be considered ineligible Is expected to require any other form of antineoplastic therapy while on study. Prior therapy with an anti-PD-1, anti-PD-L1, anti-PD-L2, anti-TIGIT, or any other antibody or drug specifically targeting T-cell costimulation or checkpoint pathways  Note: Other protocol-defined Inclusion/Exclusion criteria may apply