A framework to evaluate surrogate endpoints at the trial level: analysis in colorectal cancer

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BACKGROUND: Surrogate endpoints are increasingly used as the basis of cancer drug approvals. A strong association between treatment effects on the surrogate and true endpoint is essential for their validation as reliable endpoints. We assess the current evidence of trial-level surrogacy for colorectal cancer (CRC) endpoints through a novel framework. METHODS: We developed a framework to grade the quality of oncology surrogate endpoints in 7 domains of the surrogate relationship: data source quality (A-B); disease setting homogeneity (0-3); uniformness of surrogate and true endpoint definitions (0-3); number of trials evaluated (0-4); and individual- (0-2) and trial-level associations (0-8). We screened PubMed using keywords and medical subject headings terms for meta-analyses published before July 6, 2024, validating surrogate endpoint associations across CRC trials. Two reviewers blindly assessed each article before reaching a consensus score. The main outcomes were framework-derived evidence scores and reported trial-level associations (R2) with overall survival. RESULTS: A total of 18 articles were identified, containing 39 evaluations of 12 unique surrogate endpoints for overall survival. Evidence scores ranged from B6 to A23. Only disease-free survival consistently demonstrated high-quality evidence of trial-level surrogacy (≥A18, median R2 = 0.92). Progression-free survival and objective response rate were low-quality surrogates in metastatic CRC (progression-free survival: B6-A15, median R2 = 0.55; objective response rate: B6-A13, median R2 = 0.33). Other evaluated endpoints were demonstrated to be unreliable surrogates. CONCLUSION: Disease-free survival shows high-quality surrogacy in stage II-III colon cancer. Endpoints identified in the metastatic setting demonstrate inconsistent surrogacy evidence. Reassessment and identification of new endpoints are warranted, particularly with immunotherapy.

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