Surrogate Endpoints for Overall Survival in Immune-Oncology Trials of Advanced Gastro-Esophageal Carcinoma

BACKGROUND: We aimed to assess whether the Response Evaluation Criteria in Solid Tumors (RECIST)-based objective response rate (ORR), disease control rate (DCR) and progression-free survival (PFS) could serve as surrogate endpoints for overall survival (OS) in immune-oncology (IO) trials of advanced gastro-esophageal (GE) carcinoma. METHODS: Randomized controlled trials (RCTs) of IO that reported RECIST-based endpoints and OS in advanced GE carcinoma were screened. Surrogacy of endpoints for OS was assessed based on the correlation between endpoints with OS (arm-level), and between treatment effects on endpoints (trial-level). The correlations were quantified by Pearson correlation coefficient (R). Leave-one-out cross-validation was used to assess the prediction accuracy of surrogate model. RESULTS: Seventeen RCTs (9,657 subjects) with 20 comparisons were included. The correlations between DCR and OS were not strong at arm- (R = 0.80) and trial-levels (R = 0.45), but strong correlations between ORR (R = 0.91), PFS (R = 0.89) and OS at arm-level were observed. Treatment effect on ORR and PFS (both R = 0.71) was moderately correlated with treatment effect on OS. Leave-one-out cross-validation approach further validated the surrogacy of PFS. Our analysis showed that 3-month PFS could reliably predict 6-month OS, 6-month PFS could reliably predict 12-month OS, and 12-month PFS could reliably predict 18-month OS. The conservative minimum threshold effect of HR(PFS) was 0.73. CONCLUSIONS: PFS may be the appropriate surrogate for OS in IO trials of GE carcinoma. A conservative minimum threshold effect of HR(PFS) ≤ 0.73 has the potential to predict a significant improvement in OS.