A Bayesian predictive sample size selection design for single-arm exploratory clinical trials

The aim of an exploratory clinical trial is to determine whether a new intervention is promising for further testing in confirmatory clinical trials. Most exploratory clinical trials are designed as single-arm trials using a binary outcome with or without interim monitoring for early stopping. In this context, we propose a Bayesian adaptive design denoted as predictive sample size selection design (PSSD). The design allows for sample size selection following any planned interim analyses for early stopping of a trial, together with sample size determination before starting the trial. In the PSSD, we determine the sample size using the method proposed by Sambucini (Statistics in Medicine 2008; 27:11991224), which adopts a predictive probability criterion with two kinds of prior distributions, that is, an analysis prior used to compute posterior probabilities and a design prior used to obtain prior predictive distributions. In the sample size determination of the PSSD, we provide two sample sizes, that is, N and Nmax, using two types of design priors. At each interim analysis, we calculate the predictive probabilities of achieving a successful result at the end of the trial using the analysis prior in order to stop the trial in case of low or high efficacy (Lee et?al., Clinical Trials 2008; 5:93106), and we select an optimal sample size, that is, either N or Nmax as needed, on the basis of the predictive probabilities. We investigate the operating characteristics through simulation studies, and the PSSD retrospectively applies to a lung cancer clinical trial. (243) Copyright (c) 2012 John Wiley & Sons, Ltd.