Neurology · Medical Literature
Comparison of [18F]flortaucipir and [18F]MK6240 for the detection of tau pathology in Alzheimer's disease (HEAD): a multicentre, prospective, cross-sectional, within-participant study.
Abstract
Tau PET imaging has emerged as a critical biomarker for Alzheimer's disease, informing diagnosis, staging, and therapeutic selection. We investigated whether PET tracer selection alters tau detection. We conducted a prospective, multicentre, non-randomised, within-participant comparison of [18F]flortaucipir (Tauvid), currently used in clinical settings in the USA and Europe, and [18F]MK6240, an investigational tau PET tracer. Participants were recruited from eight north American sites and underwent tau PET, amyloid-β (Aβ) PET, and detailed cognitive assessments. Tau PET with both agents was acquired within a 45-day window. Coprimary outcomes were the discriminative accuracy for Alzheimer's disease-related cognitive impairment and the frequency of tau positivity in early medial temporal lobe (MTL) and late neocortical regions. The study is registered with ClinicalTrials.gov, NCT05361382. Between March 2, 2022, and Aug 27, 2025, 775 individuals were enrolled, with 682 completing all procedures (373 [55%] female, 309 [45%] male; 38 [6%] aged 19-27 years, 214 [31%] aged 50-65 years, and 430 [63%] aged 65-89 years). 32 (5%) participants identified as Hispanic or Latino. 637 (93%) identified as White, 24 (4%) as Black or African American, 16 (2%) as Asian, and five (1%) as other. In addition, 49 (7%) individuals were identified as being from a rural area. [18F]MK6240 showed greater accuracy than [18F]flortaucipir in distinguishing Alzheimer's disease from non-Alzheimer's disease impairment (area under the curve 0·93, 95% CI 0·89-0·95 vs 0·86, 0·75-0·91; p<0·0001). Among the older adults, tau positivity status was concordant in 560 (87%) for MTL and 603 (94%) for neocortical regions. In cognitively unimpaired participants, [18F]MK6240 identified twice as many MTL-positive cases as [18F]flortaucipir (n=54 [15%] vs n=23 [6%]). Prevalence ratio in Aβ-positive was 2·43 (95% CI 1·50-3·94; p=0·0003), identifying 23 additional cases per 100. Among discordant cases, 75 (89%) were [18F]MK6240-positive only and had higher Aβ burden (p<0·0001), APOEε4 frequency (p<0·0001), and cognitive impairment (p=0·0043) than those negative on both tracers. Neocortical tau positivity was more frequent with [18F]MK6240 than with [18F]flortaucipir in cognitively impaired individuals (80 [28%] vs 46 [16%]). Prevalence ratio in Aβ-positive was 1·74 (95% CI 1·32-2·29; p<0·0001), identifying 15 additional mild cognitive impairment and 21 dementia cases per 100. Tau PET tracer selection influences the frequency of detection of tau pathology across the ageing and Alzheimer's disease spectrum. Compared with [18F]flortaucipir, [18F]MK6240 identified more individuals with tau pathology in cognitively unimpaired and cognitively impaired individuals, with direct implications for patient stratification in clinical trials and more precise guidance for therapeutic decision-making. National Institute on Aging.
Clinical relevance
In individuals spanning the Alzheimer's disease spectrum—from cognitively unimpaired adults to those with dementia—does the investigational tau PET tracer [18F]MK6240 differ from the FDA-approved [18F]flortaucipir in its discriminative accuracy for Alzheimer's disease-related cognitive impairment and in the frequency with which it identifies tau positivity in early medial temporal lobe and late neocortical regions? __SNAPSHOT__ {"studyDesign":"Prospective, multicentre, non-randomised, within-participant cross-sectional comparative study (HEAD study; NCT05361382)","setting":"Eight North American academic and research sites, including Lawrence Berkeley National Laboratory, Mayo Clinic, McGill University, and the University of California San Francisco","sampleSize":"n=775 enrolled; n=682 completed all procedures (intervention arm 1: [18F]flortaucipir; intervention arm 2: [18F]MK6240 — both administered to every participant)","population":"Adults spanning the full Alzheimer's disease spectrum: cognitively unimpaired (CU), mild cognitive impairment (MCI), and dementia. Ages 19–89 years (63% aged 65–89); 55% female; 93% White, 4% Black or African American, 2% Asian; 5% Hispanic or Latino; 7% from rural areas. All participants also underwent amyloid-β (Aβ) PET and detailed cognitive assessment.","intervention":"[18F]MK6240, an investigational second-generation tau PET tracer with higher signal-to-noise ratio and potentially greater sensitivity for neurofibrillary tangles, particularly in medial temporal regions","comparator":"[18F]flortaucipir (Tauvid), the FDA-approved tau PET tracer in routine clinical use in the USA and Europe since 2020; both tracers were administered to every participant within a 45-day window","primaryOutcome":"Co-primary outcomes: (1) discriminative accuracy (AUC) for Alzheimer's disease-related cognitive impairment; (2) frequency of tau positivity in early medial temporal lobe (MTL) and late neocortical regions","followUp":"Cross-sectional; within-participant interval between the two tau PET scans was ≤45 days","fundingSource":"Government (National Institute on Aging)"}
Key findings
DISCRIMINATIVE ACCURACY: [18F]MK6240 demonstrated superior AUC for distinguishing Alzheimer's disease from non-Alzheimer's disease impairment compared with [18F]flortaucipir (AUC 0.93 [95% CI 0.89–0.95] vs. 0.86 [95% CI 0.75–0.91]; p<0.0001). MEDIAL TEMPORAL LOBE (EARLY) TAU POSITIVITY — COGNITIVELY UNIMPAIRED PARTICIPANTS: [18F]MK6240 identified twice as many MTL-positive cases as [18F]flortaucipir (54 [15%] vs. 23 [6%]); prevalence ratio in Aβ-positive participants: 2.43 (95% CI 1.50–3.94; p=0.0003), corresponding to 23 additional cases identified per 100 Aβ-positive CU individuals. NEOCORTICAL (LATE) TAU POSITIVITY — COGNITIVELY IMPAIRED PARTICIPANTS: Neocortical tau positivity was more frequent with [18F]MK6240 than [18F]flortaucipir (80 [28%] vs. 46 [16%]); prevalence ratio in Aβ-positive participants: 1.74 (95% CI 1.32–2.29; p<0.0001), identifying 15 additional MCI and 21 additional dementia cases per 100. CONCORDANCE: Among older adults, tau positivity status was concordant in 560 (87%) for MTL and 603 (94%) for neocortical regions. Among discordant cases, 75 (89%) were [18F]MK6240-positive only; these individuals had significantly higher Aβ burden (p<0.0001), higher APOEε4 frequency (p<0.0001), and greater cognitive impairment (p=0.0043) than those negative on both tracers—suggesting the additional detections represent true signal rather than noise. NNT/NNH: Not applicable to this diagnostic accuracy study. Adverse events: Not reported in the abstract.
Practice implications
This study establishes that tau PET tracer selection materially influences both the frequency and staging of detected tau pathology across the Alzheimer's disease spectrum. [18F]MK6240 consistently identified more individuals with tau pathology—particularly in the medial temporal lobe at early disease stages—than [18F]flortaucipir, and did so with greater discriminative accuracy for Alzheimer's disease-related cognitive impairment. Critically, discordant [18F]MK6240-only-positive cases were enriched for Aβ burden, APOEε4 carriage, and cognitive impairment, supporting biological validity of the additional detections rather than false-positive noise. These differences are clinically most consequential in MCI, when diagnostic certainty is limited and treatment decisions—including eligibility for anti-amyloid therapies—are time-sensitive. However, [18F]MK6240 is not currently FDA-approved for routine clinical use; flortaucipir remains the only approved tau PET tracer in the USA and Europe as of May 2026. Therefore, the practical implication at this time pertains primarily to clinical trial design, patient stratification, and regulatory review rather than immediate change in clinical practice. The population studied was 93% White and predominantly from academic North American sites, limiting generalizability to more diverse and community-based populations. The cross-sectional design precludes assessment of whether superior early detection by [18F]MK6240 translates into improved downstream clinical outcomes. Only the abstract was available for full methodological review; additional details on image acquisition protocols, positivity thresholds, and reader blinding were not confirmable from available sources. __LIMITATIONS__ Non-randomised within-participant design introduces potential order effects, though the 45-day window and same-scanner acquisition mitigate within-person disease progression as a confounder.,Cross-sectional design: no longitudinal follow-up to determine whether earlier tau detection by [18F]MK6240 leads to improved clinical outcomes, earlier effective intervention, or reduced dementia incidence.,Highly homogeneous sample: 93% White, predominantly from academic North American centres, markedly limiting generalizability to racially and geographically diverse real-world populations.,[18F]MK6240 is investigational and not FDA-approved; its off-target binding profile, optimal positivity thresholds, and standardisation protocols are not yet established for routine clinical use.,The superior sensitivity of [18F]MK6240 raises the question of false-positive rate: although discordant MK6240-positive cases showed corroborating biomarker abnormalities, the true positive predictive value of additional detections for clinically meaningful downstream outcomes was not assessed.,Harmonisation of tau PET signals across tracers was noted as substantially more challenging than anticipated (analogous Centiloid approach for amyloid does not readily translate), complicating cross-tracer comparisons in pooled or longitudinal analyses.,Surrogate endpoint: tau positivity is a biomarker endpoint; the study was not powered or designed to assess effects on clinical outcomes (e.g., conversion to dementia, treatment response).,Funding by the National Institute on Aging reduces, but does not eliminate, the possibility of institutional or investigator bias in tracer preference.,Full methodological detail (blinding procedures, reader criteria, threshold selection) confirmable only from the complete publication; this summary is based on the published abstract and associated reporting. __BOTTOM_LINE_CATEGORY__ potentially_practice_informing __BOTTOM_LINE__ [18F]MK6240 demonstrates superior discriminative accuracy and detects tau pathology more frequently than FDA-approved [18F]flortaucipir across the Alzheimer's disease spectrum, identifying approximately twice as many MTL-positive cases among cognitively unimpaired Aβ-positive individuals and 15–21 additional cases per 100 among cognitively impaired Aβ-positive individuals. Because [18F]MK6240 remains investigational and unapproved for routine clinical use, the immediate actionable implications are for clinical trial participant selection and regulatory prioritisation rather than a change in current clinical practice. Clinicians and trialists should recognise that tau PET tracer choice is not interchangeable and may critically determine who is identified as eligible for emerging disease-modifying therapies.