Simultaneous population enrichment and endpoint selection in phase 3 randomized controlled trials: An adaptive group sequential design with two binary alternative primary endpoints

Population enrichment designs can play a vital role in detecting treatment benefits, if present, by selecting a study population where the treatment is more likely to show a benefit compared to the unselected population. While population enrichment designs with one primary endpoint have been studied in the current literature, there are limited research on population enrichment with alternative primary endpoints. Many diseases have multiple sequelae and it can be sufficient to show treatment benefits on at least one of these consequences. In this manuscript, we provide the theoretical basis and development of a two-stage adaptive design with two binary alternative primary endpoints that simultaneously evaluates two subgroups for enrichment, selects one or both endpoints for efficacy assessments at the time of the interim analysis using pre-specified decision rules, and maintains an overall type I error rate. Treatment benefits can be declared in one or both endpoints in a selected subgroup or in the overall population at the time of interim or final analyses. We provide stage-wise boundary values for futility and efficacy and rejection probabilities under heterogeneous treatment effects in the subgroups. We further demonstrate the implementation of the proposed design and discuss venues for future development on this topic.