Here's a link to the draft guidance document. It seems targeted to helping drug companies identify and analyze multiple biomarkers or neuropsychological test results that could show benefit in slowing or halting progression towards Alzheimer's
. In addition to using preclinical diagnostic stages (which I would guess will become common in reporting study participants at baseline and results), this notes that improvements even when comparing preclinical participants, could result in "accelerated approval" for drug treatments, pending further research to support the final endpoint (patients without treatment reaching clinical MCI or AD). This seems to be a recognition that as the pre-clinical physiological changes are better understood, it could be possible to thwart those changes as compared to a similar placebo group.
To use the analogy of football concussions: if you can show that having no concussions results in athletes with far better scores on memory, information processing speeds and emotional regulation than athletes who have had multiple concussions, you don't need to wait 40 years to autopsy their brains and diagnoses CTE. You can just get rid of the damn concussions. Maybe someday soon, through lifestyle interventions and drugs, where needed, we can just get rid of the damn precursors to AD. https://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM596728.pdf
Early Alzheimer’s Disease: Developing Drugs for Treatment Guidance for Industry
DRAFT GUIDANCE This guidance document is being distributed for comment purposes only.
[Lines 228-233] In Stage 1 patients, an effect on the characteristic pathophysiologic changes of AD, as demonstrated by an effect on various biomarkers, may be measured. Such an effect, analyzed as a primary efficacy measure, may, in principle, serve as the basis for an accelerated approval (i.e., the biomarker effects would be found to be reasonably likely to predict clinical benefit, with a post-approval requirement for a study to confirm the predicted clinical benefit).