Group sequential methods for comparison of cure rates in clinical trials.

Since a subset of the patient population may be cured of disease in some clinical trials, one might be more interested in testing the differences in cure rates rather than other types of differences in failure distributions. Also, the monitoring of clinical trial results frequently necessitates the use of repeated examination of outcome for ethical and efficiency reasons. Parametric and non-parametric group sequential methods are proposed for comparing the cure rates between two treatment groups at the interim analyses during the trial. In both methods, construction of the group sequential boundaries is based on the asymptotic joint distribution of the sequentially computed statistics and their covariance matrix. The proposed methods are illustrated with a pediatric cancer trial which had been conducted by the Childrens Cancer Group.