INTRODUCTION: This study uses longitudinal amyloid biomarker and cognitive data to generate sample size estimates for two-armed, pre-clinical amyloid clearance clinical trials. METHODS: PET PiB DVR ranges defined three amyloid groups (positive, "A+"; sub threshold/low positive, "subA+"; and negative, "A-") in cognitively unimpaired Wisconsin Registry for Alzheimer's Prevention participants. Amyloid group trajectories estimated from mixed effects models informed per-treatment-arm sample size estimates to detect plausible treatment effects over 3-year (biomarker) or 6-year (cognition) study windows (80% power). RESULTS: To detect ≥60% slowing in PiB accumulation, ≤40 may be needed per arm for both SubA+ and A+; to detect the same effect sizes in plasma p-tau217 trajectories, ~50-1700 are needed, depending on assay and amyloid subgroup. Among cognitive outcomes, Digit Symbol Substitution and a 5-test Preclinical Alzheimer's Cognitive Composite consistently required fewest (<2000) per arm. DISCUSSION: Early intervention study planning will benefit from selection of outcomes that are most sensitive to AD biomarker-related preclinical change.
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Koscik et al. (2025) studied this question.