[Validation of surrogate endpoints in digestive oncology]

In oncology, overall survival is often referred to as the gold standard for the evaluation of a novel therapy in phase III clinical trials. The use of an earlier endpoint (intermediate endpoint) would allow to reduce the duration, the number of patients and/or the cost of the studies. Before being used as primary endpoint, it has to be validated as surrogate for overall survival. Two main statistical methods have been developed. The first evaluates the proportion of treatment effect on overall survival that can be attributable to the effect on the surrogate endpoint. The second, the meta-analytic approach, estimates the correlation between the treatment effect on the surrogate and its effect on overall survival, based on the results of previous completed trials. It allows, for a future trial, the prediction of the expected effect on overall survival according to the observed effect on the surrogate. To date, in digestive oncology, only progression-free survival for the treatment of advanced colon cancers and disease-free survival in the adjuvant setting have been validated as surrogate endpoints for overall survival.