Lecanemab was the first amyloid-targeting monoclonal antibody approved by the European Commission for treating patients with mild cognitive impairment (MCI) and mild dementia due to Alzheimer’s disease (AD). While this marketing authorization led to heterogeneous situations across European countries, France declined reimbursement, citing limited clinical benefit and concerns about the healthcare system’s capacity to implement this new care pathway. This capacity depends directly on the number of eligible patients, yet robust estimates remain limited and highly variable across studies. Our objective was therefore to estimate the population eligible for lecanemab in France.

Using transportability methods based on inverse odds of selection weighting, we articulated the nationwide consultation data from the French National Alzheimer Database (BNA) with the deeply phenotyped MEMENTO clinical cohort. Eligibility for lecanemab followed the French appropriate use recommendations: 1) clinical eligibility (age 50–90 years, MCI with common AD phenotype or mild AD dementia, MMSE ≥22), 2) biological eligibility (amyloid confirmation determined sequentially using plasma p-tau217, cerebrospinal fluid biomarkers and amyloid-PET), 3) absence of contraindications (APOEε4 homozygosity, anticoagulant use, MRI risk markers for ARIA).

Among patients consulting French memory clinics, 19.5% met clinical eligibility criteria. Of these, 73.0% (95%CI: 67.6–77.9) were amyloid-positive, and 49.7% (95%CI: 44.0–55.5) remained eligible after applying safety criteria. Overall, 9.7% (95%CI: 8.6–10.8) of patients consulting memory clinics were estimated to be eligible for lecanemab, representing approximately 18,200 individuals nationally (annual average, 2022–2024).

These results inform healthcare planning for disease-modifying therapy implementation in France and comparable countries.