Single-arm phase IIA clinical trials with go/no-go decisions.

Phase IIA clinical trials are commonly conducted as pilot studies to evaluate efficacy and safety in selected populations of patients with the disease or condition to be treated or prevented. The efficacy objective is to find preliminarily evidence of the effectiveness or ineffectiveness of study treatments. Go/no-go decisions will be made during or at the end of these trials. Interim analyses (multiple stages) are usually built-in to terminate futile treatments. The designs presented in this paper match the efficacy objective with go/no-go decisions. This is achieved by setting up the threshold as the minimal effective response rate. Asymmetric type I error spending at this threshold is also possible. When two-stage designs are used, the stage I sample size is flexible and can cover all practical scenarios.