Clinical trials require significant resources to complete in terms of patients, investigators, and time and should be carefully designed and conducted so that they use the minimum amount of resources necessary to answer the motivating clinical question. The size of a clinical trial is typically based on the minimum number of patients required to have high probability of detecting the anticipated treatment effect. However, it is possible that strong evidence could emerge earlier in the trial either in favor of or against the benefit of the novel treatment. If early trial results are compelling, stopping the trial before the maximum planned sample size is reached presents ethical advantages for patients inside and outside the trial and can save resources that can be redirected to other clinical questions. This advantage must be balanced against the potential for overestimation of the treatment effect and other limitations of smaller trials (eg, limited safety data, less information about treatment effects in subgroups).
Kert Viele, Anna McGlothlin, Kristine Broglio. Interpretation of Clinical Trials That Stopped Early. JAMA. 2016;315(15):1646–1647. doi:10.1001/jama.2016.2628