Disease-free survival as a surrogate for overall survival in neoadjuvant trials of gastroesophageal adenocarcinoma: Pooled analysis of individual patient data from randomised controlled trials

Abstract

Introduction: Disease-free survival (DFS) is increasingly being used as surrogate end-point for overall survival (OS) in cancer trials. So far, there has been no validation of the surrogacy of DFS for OS for neoadjuvant treatment of gastroesophageal adenocarcinoma.

Methods: The study uses individual patient data (IPD) from eight randomised controlled trials (RCTs) (n = 1126 patients) comparing neoadjuvant therapy followed by surgery with surgery alone for gastroesophageal adenocarcinoma. Correlation between OS time and DFS time was calculated to evaluate individual-level surrogacy. For each trial, survival curves using the Kaplan-Meier method were plotted and hazard ratios (HRs) on the treatment effects were calculated for OS and DFS separately. Those HRs were pooled in a random-effects meta-analysis. Observed HRs were compared with predicted HRs for OS using results from an error-in-variables linear regression model accounting for the uncertainty about the estimated effect. The strength of the association was quantified by the coefficient of determination to assess trial-level surrogacy. The surrogate threshold effect was calculated to determine the minimum treatment effect on DFS necessary to predict a non-zero treatment effect on OS.

Results: A strong correlation between OS time and DFS time was observed, indicating a high individual-level surrogacy. For all RCTs, estimated HRs for OS and DFS were highly similar. In the meta-analysis, the overall HR for OS was virtually identical to that for DFS. The estimated coefficient of determination r² for the association between HRs for OS and DFS was 0.912 (95% confidence interval: 0.75-1.0), indicating a very good fit of the regression model and thus a strong trial-level surrogacy between OS and DFS. The surrogate threshold effect based on the regression analysis was 0.79.

Discussion: Based on strong correlations between DFS and OS, as well as a strong correlation of the treatment effects of the two end-points in the error-in-variable regression, DFS seems an appropriate surrogate marker for OS in randomised trials of neoadjuvant chemotherapy or chemoradiotherapy for gastroesophageal adenocarcinoma.

Keywords: Disease-free survival; Gastroesophageal adenocarcinoma; Individual patient data meta-analysis; Neoadjuvant chemoradiotherapy; Neoadjuvant chemotherapy; Overall survival.