Tislelizumab (TIS) + chemotherapy (CT) vs placebo (PBO) + CT as first-line treatment for locally advanced (LA), unresectable esophageal squamous cell carcinoma (ESCC): PD-L1 tumor area positivity (TAP) score ≥1% subgroup analysis of RATIONALE-306.

Abstract

381 Background: In RATIONALE-306 (NCT03783442), patients (pts) with LA unresectable or metastatic ESCC who received TIS (intravenously, 200 mg, every 3 weeks) + CT (platinum + fluoropyrimidine or paclitaxel) had longer median overall survival (OS) than pts who received PBO + CT at the interim analysis; improvement was maintained after a ≥3-year follow-up. Post hoc analyses in the PD-L1 TAP ≥1% subgroup showed clinically meaningful improvement with TIS + CT. These data supported the US FDA approval for unresectable or metastatic ESCC. Here we report the subgroup analysis of pts who had LA ESCC with PD-L1 TAP score ≥1%. Methods: Pts who had LA unresectable ESCC with PD-L1 TAP score ≥1% were included in this post hoc analysis. Efficacy outcomes (OS, progression-free survival [PFS], objective response rate [ORR], duration of response [DoR]) and safety were analyzed. Results: At data cutoff (Feb 28, 2022), of 649 pts randomized, 63 had LA ESCC with PD-L1 TAP score ≥1% (TIS + CT n=31; PBO + CT n=32; median age 67.0 years; 85.7% male). At median follow-up (TIS + CT 24.4 months; PBO + CT 24.5 months), efficacy with TIS + CT was improved vs PBO + CT (Table) and was consistent with the intent-to-treat (ITT) population. Efficacy was maintained after a ≥3-year follow-up (data cutoff: Nov 24, 2023; Table). Conclusions: In this post-hoc analysis, the median OS for pts receiving TIS + CT exceeded two years. The regimen was well tolerated. While the findings require validation in future clinical trials, first-line TIS + CT is an encouraging option for pts who have LA unresectable ESCC with PD-L1 TAP score ≥1%. Clinical trial information: NCT03783442 . Interim Analysis 3-Year Follow-up TIS + CT (n=31) PBO + CT (n=32) TIS + CT (n=32) e PBO + CT (n=31) f Median OS, mo(95% CI) 25.6 (15.3, NE) 11.5(9.0, 21.8) 25.6 (15.3, NE) 12.3(9.0, 21.8) HR (95% CI) a 0.36 (0.17, 0.77) – 0.50 (0.26, 0.95) – Median PFS, a mo(95% CI) 13.2(6.8, NE) 6.7(4.2, 9.7) 13.2(6.8, 27.7) 6.7(4.2, 9.7) HR (95% CI) a 0.46 (0.22, 0.96) – 0.47 (0.23, 0.96) – ORR, b,c n (%) 18 (58.1) 10 (31.3) 19 (59.4) 10 (32.3) Median DoR, b,d mo(95% CI) Not reached (8.4, NE) 5.7 (1.5, 9.6) 22.1 (6.1, NE) 5.7 (1.5, 9.6) a Stratified. b Investigator assessed. c Unconfirmed. d Based on unconfirmed ORR. e One patient’s disease status at baseline was changed to LA after interim analysis. f One patient’s disease status at baseline was changed to metastatic after interim analysis. NE, not estimable.