Platform trials are a more efficient way of testing multiple treatments compared to running separate trials. In this paper we consider platform trials where, if a treatment is found to be superior to the control, it will become the new standard of care (and the control in the platform). The remaining treatments are then tested against this new control. In such a setting, one can either keep the information on both the new standard of care and the other active treatments before the control is changed or one could discard this information when testing for benefit of the remaining treatments. We will show analytically and numerically that retaining the information collected before the change in control can be detrimental to the power of the study. Specifically, we consider the overall power, the probability that the active treatment with the greatest treatment effect is found during the trial. We also consider the conditional power of the active treatments, the probability a given treatment can be found superior against the current control. We prove when, in a multi-arm multi-stage trial where no arms are added, retaining the information is detrimental to both overall and conditional power of the remaining treatments. This loss of power is studied for a motivating example. We then discuss the effect on platform trials in which arms are added later. On the basis of these observations we discuss different aspects to consider when deciding whether to run a continuous platform trial or whether one may be better running a new trial.

翻译：平台试验相较于独立开展多个试验，是一种更高效的测试多种治疗方法的方式。本文考虑一种平台试验场景：当某种疗法被证实优于对照疗法时，该疗法将成为新的标准治疗方案（并作为平台中的新对照），其余在研疗法随后将与这一新对照进行比较。在这种设定下，研究者可以选择保留对照变更前关于新标准治疗方案及其他在研疗法的全部数据，也可以选择在评估剩余疗法获益时丢弃这些数据。我们将通过解析推导和数值模拟证明：保留对照变更前收集的数据反而可能降低研究的检验效能。具体而言，我们重点分析了总体检验效能（即在试验过程中识别出疗效最优的在研疗法的概率），以及在研疗法的条件检验效能（即特定疗法相对于当前对照被证实具有优效性的概率）。我们证明了在多臂多阶段试验（未添加新试验臂）中，保留既往数据会同时损害剩余疗法的总体检验效能和条件检验效能。通过一个激励性案例研究了检验效能的损失程度，并进一步探讨了后期添加新试验臂时该效应对平台试验的影响。基于上述发现，我们讨论了决定是否开展连续性平台试验（或是否应启动全新试验）时需权衡的多维度考量因素。