Group sequential designs for cure rate models with early stopping in favour of the null hypothesis

Ewell and Ibrahim derived the large sample distribution of the logrank statistic under general local alternatives. Their asymptotic results enable us to extend several group sequential designs which allow for early stopping in favour of the null hypothesis to the setting in which the cure rate model is appropriate. In particular, we derive stopping rules for the cure rate model using conditional power, predictive power and repeated confidence intervals methods. We illustrate the methods proposed using a hypothetical phase III clinical trial which is typical for melanoma studies.