Adaptive designs at European Organisation for Research and Treatment of Cancer (EORTC) with a focus on adaptive sample size re-estimation based on interim-effect size.

Given the high failure rates and the increased costs of Phase III trials in oncology and the recent explosion of targeted agents, researchers are looking for better design strategies to try and optimise the use of available patients and financial resources. In this context, adaptive designs are seen as promising tools. We reviewed the different possible adaptations in the design of a clinical trial on the basis of the FDA guidance and summarized these. The pro and cons of adaptive designs are highlighted with a focus on one of the more 'controversial' adaptive designs, the sample size reassessment based on interim-effect size as proposed by Mehta and Pocock. While group sequential designs are preferable to such adaptive designs, both are difficult to implement in the case of rapid accrual and long time to event. Adaptive designs may have some potential in less favourable situations. However, the increase in overall power should be carefully weighted as well as the risk of a large negative trial. Adaptive designs need good, sometimes extensive, logistics. Some adaptive designs (e.g. group sequential designs) proved to be very useful and are already a part of the standard repertoire of trial designs used at European Organisation for Research and Treatment of Cancer (EORTC). Adaptive designs need strong measures to prevent bias that could otherwise become uncontrollable, particularly if interim results are leaked. This includes a prospective planning of adaptations. Finally, these studies currently have the potential to induce a heavy workload and cost linked to their regulatory management.