First-Line Tislelizumab Plus Chemotherapy for Esophageal Squamous Cell Carcinoma with Programmed Death-Ligand 1 Expression ≥ 1%: A Retrospective Analysis of RATIONALE-306

IntroductionThe United States Food and Drug Administration Oncologic Drugs Advisory Committee voted (September 2024) against the use of programmed cell death protein-1 inhibitors for first-line treatment of advanced or metastatic unresectable esophageal squamous cell carcinoma (ESCC) with a programmed death-ligand 1 (PD-L1) expression Tumor Area Positivity (TAP) score < 1% or combined positive score < 1 due to an unfavorable benefit-risk profile observed across the phase 3 CheckMate 648, KEYNOTE-590, and RATIONALE-306 trials. Therefore, we conducted a retrospective analysis of RATIONALE-306 to evaluate the efficacy and safety of tislelizumab plus investigator-chosen chemotherapy (ICC) versus placebo plus ICC in patients with advanced or metastatic unresectable ESCC and a PD-L1 TAP score >= 1%. MethodsAdult patients with advanced or metastatic unresectable ESCC enrolled in the global, randomized, phase 3 RATIONALE-306 trial randomly received tislelizumab 200 mg every 3 weeks plus ICC or matched placebo plus ICC. Efficacy and safety outcomes were evaluated among patients who were retrospectively assessed for PD-L1 expression defined by a TAP score >= 1%. ResultsAt primary analysis data cutoff (February 28, 2022), a clinically meaningful improvement in median overall survival was observed among 230 patients in the tislelizumab plus ICC arm {16.8 [95% confidence interval (CI) 15.3-20.8] months} versus 248 patients in the placebo plus ICC arm [9.6 (95% CI 8.9-11.8) months] [stratified hazard ratio 0.64 (95% CI 0.51-0.80)]; this was maintained at a 3-year follow-up data cutoff (November 24, 2023). Similar findings at primary analysis were observed for progression-free survival, objective response rate, disease control rate, and duration of response. Tislelizumab plus ICC was tolerable and no new safety signals were observed. ConclusionsTislelizumab plus ICC is an effective and well tolerated first-line treatment option for patients with advanced or metastatic unresectable ESCC and a tumor PD-L1 TAP score >= 1%. Trial Registration NumberClinicalTrials.gov NCT03783442.