Optimal seamless phase 2/3 oncology trial designs based on Probability of Success (PoS).

In recent years, there has been an increasing trend in conducting seamless phase 2/3 clinical trials for drug development in the pharmaceutical industry due to the visible advantages compared with traditional approaches for separate phase 2 and 3 development. Innovative study designs have been proposed for seamless phase 2/3 trials, which mainly focus on the traditional aspects of study design, such as how to control the Type I error rate, sample size re-estimation after the phase 2 portion, and how to make treatment selection at the end of the phase 2 portion. However, there are still some questions unresolved such as how to determine the go/no-go boundary and how to plan the phase 2 portion sample size. In this paper, we discuss how to determine the phase 2 portion and phase 3 portion sample sizes as well as the corresponding go/no-go criteria for a seamless phase 2/3 oncology trial based on Probability of Success. In addition, we further expand the methodology to include designs with an interim look within the phase 2 portion to speed up the go/no-go decision-making process. In case of overwhelming efficacy, this design would further shorten the overall trial duration. In case of inefficacy, this design can stop the trial earlier without exposing more patients to inefficacious treatment.