Tislelizumab Plus Platinum and Etoposide Versus Placebo Plus Platinum and Etoposide as First-Line Treatment for Extensive-Stage Small Cell Lung Cancer (RATIONALE-312): a Multicenter, Double-Blind, Placebo-Controlled, Randomized, Phase 3 Clinical Trial

Extensive-stage SCLC (ES-SCLC) prognosis remains poor. The phase 3 RATIONALE-312 study aimed to evaluate the efficacy and safety of tislelizumab plus chemotherapy as first-line treatment for ES-SCLC.RATIONALE-312 is a randomized, double-blind, placebo-controlled trial, conducted in the People's Republic of China. Eligible patients with previously untreated ES-SCLC were randomized 1:1 to receive four cycles of tislelizumab 200 mg or placebo, with etoposide plus carboplatin or cisplatin intravenously every 3 weeks, followed by tislelizumab 200 mg or placebo as maintenance. The primary end point was overall survival (OS). Secondary end points included progression-free survival and safety.Between July 22, 2019 and April 21, 2021, 457 patients were randomized to tislelizumab (n = 227) or placebo (n = 230), plus chemotherapy. Baseline demographics were generally balanced between arms. At the data cutoff (April 19, 2023), the median study follow-up was 14.2 months (interquartile range: 8.6-25.3). Tislelizumab plus chemotherapy exhibited a statistically significant OS benefit versus placebo plus chemotherapy (stratified hazard ratio = 0.75 [95% confidence interval (CI): 0.61-0.93]; one-sided p = 0.0040; median: 15.5 [95% CI: 13.5-17.1] versus 13.5 mo [95% CI: 12.1-14.9], respectively). Progression-free survival was significantly improved in the tislelizumab versus placebo arm (stratified hazard ratio = 0.64 [95% CI: 0.52-0.78]; p < 0.0001; median: 4.7 [95% CI: 4.3-5.5] versus 4.3 mo [95% CI: 4.2-4.4], respectively). Grade greater than or equal to 3 treatment-related adverse events were reported in 86% of patients in each treatment arm and were mostly hematologic.Tislelizumab plus chemotherapy exhibited statistically significant clinical benefit and manageable safety compared with placebo plus chemotherapy as first-line treatment in patients with advanced ES-SCLC.