Bayesian approach to two-stage phase II trial

Consider the situation in which there are several different therapeutic agents. It is desired to select the best agent and to examine its efficacy relative to the control. Too often clinical trials terminate with negative outcomes in part due to inadequate phase II studies. A two-stage phase II based on a Bayesian approach is considered in order to reduce such likelihood. The first stage consists of selecting the best agent and the second stage consists of examining the relative efficacy of the selected agent compared to the control. A formal phase III clinical trial can be initiated when the particular agent is shown to be promising on the basis of the proposed phase II study. The Bayesian approach employed uses an ad hoc likelihood due to the fact that the exact likelihood is complex and intractable. In this sense the proposed approach is thus an approximation. A simulation study is conducted to investigate the performance of the proposed Bayesian approach and compared to two fixed-sample-size approaches. Due to the fact that the procedure is approximate, the simulation study is essential to assess the usefulness of the procedure. The study suggests that the Bayesian approach is an attractive alternative to fixed-sample-size approaches.