Reviews/Anti Amyloid Antibodies/Lecanemab and donanemab clear amyloid
Amyloid · AMAB-AMY-01 · v2
This claim asks only whether two antibody drugs, lecanemab and donanemab, lower the amount of amyloid plaque in the brains of people with early Alzheimer's disease. For lecanemab the corpus is strong and direct: a large phase 3 randomised trial measured a clear fall in brain amyloid on PET imaging [3], the same programme showed the reduction held up to 36 months [2], and a separate real-world group of patients showed amyloid falling again [7]. For donanemab the corpus carries one primary analysis reporting robust plaque reduction and clearance [19], so the evidence is real but rests on far less in this corpus than lecanemab's. The panel also noted that the measured thing is a fall in a PET tracer signal, which is read as plaque reduction rather than directly seen as physical plaque removal. Because the claim is about the measured plaque surrogate itself, not about clinical benefit, the panel treated the evidence as directly on point.
The phase 3 Clarity AD trial directly measured brain amyloid in a 698-participant PET substudy and reported a difference of -59.1 centiloids favouring lecanemab [3]. Durability of amyloid suppression was reported in the 36-month open-label extension [2], and an independent multicentre real-world Chinese cohort of 261 patients reported amyloid PET clearance of mean -22.1 Centiloid with 29.2% turning amyloid-negative [7]. The Clarity AD Asian regional cohort of 294 subjects reported reduction in brain amyloid consistent with the overall population [4]. For donanemab, a population-pharmacokinetic analysis of phase Ib and phase 2 TRAILBLAZER-ALZ data reported robust amyloid plaque reduction, with most participants achieving amyloid clearance below 24.1 Centiloids by 52 weeks [19]. The contested point: The division is in triangulation and wording, not direction: donanemab's amyloid evidence here rests on a single population-PK paper [19] drawn from phase Ib and phase 2 data, with no phase 3 primary readout in the corpus, whereas lecanemab is carried by a randomised PET substudy [3] plus corroboration [2][4][7]. Separately, the endpoint is a fall in amyloid-PET tracer uptake, and reading reduced tracer signal as physical plaque removal is an interpretive step [17].
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One reviewer's only job is to attack the finding. The challenges below were weighed before the grade was set.
Donanemab's included primary amyloid evidence rests on a single pharmacokinetic analysis [19] of phase Ib and phase 2 data; the phase 3 TRAILBLAZER-ALZ2 primary readout is not present in the eligible corpus, so the donanemab leg is far less triangulated than the lecanemab leg.
The claim asserts reduction of 'amyloid plaques', but the measured endpoint is amyloid-PET tracer uptake (centiloids); equating reduced tracer signal with physical plaque removal is an interpretive step, making the wording slightly over-read the surrogate.
Where it remains uncertain. Donanemab's amyloid evidence in this corpus rests on a single population-PK analysis of phase Ib and phase 2 data [19] rather than a phase 3 primary readout, and the endpoint is a tracer signal read as plaque removal [17].
Aleatory
Time to donanemab amyloid clearance varied with baseline level, with higher baseline levels leaving fewer participants achieving clearance [19]; the Chinese cohort saw only 29.2% turn amyloid-negative [7].
Epistemic
The donanemab amyloid evidence rests on one population-PK analysis of phase Ib and phase 2 data [19]; no phase 3 TRAILBLAZER-ALZ2 primary readout is present in the corpus.
Inferential
The measured endpoint is amyloid-PET tracer uptake in centiloids [3][19]; reading reduced tracer signal as physical plaque removal is interpretive, and one source argues the reduced uptake may partly reflect therapy-related tissue damage [17].
The load-bearing papers from a corpus of 20, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
Demonstrates durability of lecanemab amyloid suppression to 36 months.
“Results presented in our paper demonstrate that lecanemab continued suppression of amyloid plaque levels and significantly slowed clinical decline on multiple measures of cognition, function, and quality of life in early AD at 18 months and continued for 36 months to date.”
Panel auditInternal validity: medium · scope of inference: Long-term lecanemab in early symptomatic AD.Key limitations: open-label, uncontrolled for amyloid · no amyloid number · donanemab not addressed
Quantified, randomised, placebo-controlled evidence of lecanemab amyloid reduction in early AD.
“In a substudy involving 698 participants, there were greater reductions in brain amyloid burden with lecanemab than with placebo (difference, -59.1 centiloids; 95% CI, -62.6 to -55.6).”
Panel auditInternal validity: high · scope of inference: Lecanemab in persons 50-90 with MCI or mild dementia due to AD and confirmed amyloid.Key limitations: amyloid measured in substudy subset (698) · 18-month horizon · donanemab not addressed
Independent real-world corroboration of lecanemab amyloid PET clearance in early AD.
“a p‑tau217 reduction correlated with amyloid PET clearance (mean -22.1 Centiloid; 29.2% turned amyloid-negative).”
Panel auditInternal validity: low · scope of inference: Real-world lecanemab in Chinese patients from MCI to moderate dementia.Key limitations: population extends to moderate dementia beyond early AD · amyloid uncontrolled · optional PET subset
Subgroup corroboration of lecanemab amyloid reduction consistency.
“lecanemab demonstrated a consistent slowing of decline in clinical (global, cognitive, functional, and quality of life) outcomes, and reduction in brain amyloid in early Alzheimer's disease.”
Panel auditInternal validity: medium · scope of inference: Lecanemab in the Asian-region early AD subgroup.Key limitations: no amyloid magnitude for subgroup · subgroup underpowered · donanemab not addressed
4 of 20 papers shown. The full review lists all of them, with the panel’s arbitration →
Claims are graded at each quarterly release, and re-graded between releases only when a pivotal trial lands. Every change is a new version of the claim.
Both named drugs have direct, primary, PET-measured evidence of amyloid plaque reduction in the exact early-AD population, with the only real limiter being donanemab's thinner primary-paper base in this corpus.
Release 2026-q4 re-graded every claim from its corpus under protocol v0.19. An earlier release's grade is shown for the record; it came from an earlier protocol and is not a movement.
Assumptions that carry weight but are not themselves established.
The panel records the gap that would most move the claim, and the study that would close it.
Donanemab phase 3 primary amyloid readout. Donanemab's amyloid evidence here is a single population-PK paper [19], leaving its leg far less triangulated than lecanemab's. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: Include the phase 3 TRAILBLAZER-ALZ2 primary amyloid-PET readout reporting change from baseline in centiloids for donanemab in early AD.
Open question: Does donanemab reduce brain amyloid in early AD when measured in a phase 3 primary amyloid-PET endpoint? Why it is still open: The only donanemab amyloid source in the corpus is a population-PK analysis of phase Ib and phase 2 data [19]; the phase 3 primary readout is absent.
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 21 Oct 2026 · protocol v0.19