This Phase 3 study was a randomized, double-blind, placebo-controlled, multicenter trial designed to evaluate the efficacy of tislelizumab in combination with either cisplatin or carboplatin and etoposide (Arm A), compared to placebo combined with either cisplatin or carboplatin and etoposide (Arm B), as a first-line treatment for participants with previously untreated extensive-stage small cell lung cancer (ES-SCLC).