Initially, we used systematic reviews/searches to aid the interpretation and reporting of the results of MRC CTU cancer trials in light of other evidence. Subsequently, we have synthesised external evidence, to provide the rationale for new trials or protocol modifications for ongoing trials, for example, in response to new predictive biomarkers emerging during their conduct. Currently, systematic reviews are informing adaptations to our ongoing, multi-arm, multi-stage cancer trials, for example, to select the most appropriate therapies for new arms. We also plan to use prospective, retrospective and network meta-analyses of aggregate data and IPD, to tailor evidence synthesis to the specific needs of our ongoing trials, in the context of other trial evidence. We will present examples of evidence synthesis informing lung, colorectal, breast, upper GI and prostate cancer trials.