Clinical trial end points: on the road to nowhere?

Over the past decade, there have been an increasing number of therapeutic clinical trials of PD. Despite many of these trials showing a positive treatment effect, few have resulted in clear and unambiguous recommendations regarding clinical practice, unlike trials of cerebrovascular disease. The authors hypothesize that lingering therapeutic uncertainty exists because many of the clinical trial end points have been surrogate outcome measures rather than end points with clear and convincing value to patients. The theoretical advantage of using validated surrogate outcomes in definitive trials includes smaller, faster, and less expensive studies. Consequences of using surrogate outcomes that have not been validated include ambiguous evidence and wasted resources as well as patient harm and missed opportunities. To optimize the chance that future trial results will provide clear treatment verdicts and to take full advantage of exciting developments in biomarker technology such as SPECT and PET, it is becoming progressively more urgent to understand the proper role, use, and challenges of using surrogate outcome measures in PD therapeutics.