Are biomarkers harmful to recruitment and retention in Alzheimer's disease clinical trials? An international perspective.

Clinical trials in Alzheimer's disease (AD) do not only generate high costs but have also been of little success within recent years. The failure of several large phase III clinical trials on highly promising disease modifying compounds calls for a critical reflection on potential reasons and counter-measures. The recent introduction of new diagnostic criteria of AD and the development and validation of diagnostic and predictive AD biomarkers allows enriching study populations, reducing variance, and improving statistical power of trials while even opening the possibility to reduce total study costs. While CSF or extensive imaging biomarkers might adversely affect retention in clinical trials, their careful application will unlikely reduce adherence. Regulatory authorities are generally supportive of biomarker use in clinical trials but potential consequences of biomarker based patient selection on the generalizability of trial results need careful evaluation.