Comparison of anticipated and actual control group outcome in randomised trials in paediatric oncology provides evidence that non-randomised studies are biased in favour of the novel treatment

Introduction Historically controlled studies (HCSs) compare data from two or more separately conducted studies – the new treatment arm, usually prospectively collected, is compared to a control arm of retrospective data. HCSs are frequently undertaken in paediatric oncology (PO), where there is a widespread belief that RCTs cannot be performed in rare diseases. This is despite the potential biases in HCSs being well known – e.g. other factors change over time.