Combining tumour response and progression free survival as surrogate endpoints for overall survival in advanced colorectal cancer

Progression free survival (PFS) and tumour response (TR) have been investigated as surrogate endpoints for overall survival (OS) in advanced colorectal cancer (aCRC), however their validity has been shown to be suboptimal. In recent years, meta-analytic methods allowing for use of multiple surrogate endpoints jointly have been proposed. The aim of this research was to assess if PFS and TR used jointly as surrogate endpoints to OS improve their predictive value. Data were obtained from a systematic review of randomised controlled trials investigating effectiveness of different pharmacological therapies in aCRC: systemic chemotherapies, anti-epidermal growth factor receptor therapies, anti-angiogenic agents, other multi-targeted antifolate treatments and intra-hepatic arterial chemotherapy. Multivariate meta-analysis was used to model the association patterns between treatment effects on the surrogate endpoints (PFS, TR) and the final outcome (OS). Analysis of 33 trials which reported treatment effects on all three outcomes showed reasonably strong association between treatment effects on PFS and OS. A weak surrogate relationship was noted between the treatment effects on TR and OS. Modelling the two surrogate endpoints, TR and PFS, jointly as predictors of OS gave no marked improvement in neither surrogacy patterns nor the precision of predicted treatment effect in the cross-validation procedure. When investigating subgroups of therapy, only small improvement in precision of predicted treatment effects on the final outcome in studies investigating anti-angiogenic therapy was noted. Overall, the simultaneous modelling of two surrogate endpoints did not lead to improvement in association between treatment effects on surrogate and final endpoints in aCRC.