A note on penalty-free interim analyses of clinical studies with binary responses

In oncology studies with binary responses, it is often desirable to demonstrate the anti-tumor activity of a test drug before the planned study completes. We propose penalty-free interim analysis strategies that do not change the rejection criterion for the test of null hypothesis at the end. The strategies are applied to standard one-arm and two-arm studies. Although the motivating studies are from oncology, the findings in this research note are equally applicable to similar settings. A broad list of references is provide to stimulate further research on the topic.