Biomarkers in Alzheimer's disease: not yet surrogate endpoints.

Clinical tests are currently used as endpoints in Alzheimer's disease (AD) trials to measure disease progression based on cognitive, functional, or overall decline. These endpoints are not a perfect reflection of the underlying disease pathology and may be insensitive to disease progression, especially in early AD. Furthermore, they are subject to high variability, leading to large sample sizes and long trial durations. A biomarker that could better reflect AD progression and also predict clinical benefits of drug treatments-a surrogate endpoint-would be of great use. Currently, no surrogate endpoints have been validated in AD. Structural imaging seems to be a better candidate than plasma or CSF biomarkers, but is not yet validated as a surrogate endpoint. More prospective clinical trials are needed for the validation process. While AD biomarkers cannot currently be used as formal surrogate markers, they may nonetheless be useful measures in clinical trials alongside clinical outcomes.