Lecanemab, an intravenous treatment that targets amyloid protein buildup in the brain, was the first disease-modifying therapy for early Alzheimer’s disease (AD) to be authorised in Europe. The positive opinion from the European Medicines Agency was based on 18 months of data collected during the CLARITY-AD Phase 3 trial of lecanemab, which evaluated the safety and efficacy of the drug in almost 1,800 participants. At the 2025 Alzheimer’s Association International Conference (AAIC), clinical experts presented interim data from the Open Label Extension of CLARITY-AD – showing continued efficacy over 4 years.
Lecanemab received traditional approval from the US Food and Drug Administration in July 2023, for the treatment of mild cognitive impairment (MCI) or mild dementia due to AD. At AAIC, experts presented data from 178 individuals with early AD, who were treated with lecanemab as part of the American open label extension (OLE) to CLARITY-AD. The average age of participants was 74.2 years, and a majority (57.6%) had a diagnosis of MCI due to AD. Of the 178 patients, amyloid-related imaging abnormalities (ARIA; a side effect linked to small bleeds or swelling in the brain) were observed in 12.9%, with no serious bleeding events or deaths reported. Overall, around 76% of patients remained at the same clinical stage, with 6.7% showing clinical improvement, going from mild dementia to MCI.
The company also presented real-world data on the impact of ApoE4 status on long-term safety and efficacy of lecanemab. As well as being a genetic risk factor for AD, carrying two copies of ApoE4 confers a substantially higher risk of ARIA during treatment with anti-amyloid antibodies. In the core CLARITY-AD study, 45% of participants carrying two copies of ApoE4 experienced ARIA, over double the rate of participants carrying a single copy of ApoE4 (19%). In the group evaluated during the OLE, the incidence of ARIA in participants with two ApoE4 copies was lower, at 20%. A similar, lower trend was observed for people with one or no copies of ApoE4. Looking at the 4-year efficacy of lecanemab in people with different ApoE4 genotypes, patients with one or no copies of ApoE4 were more likely to remain stable or improve (88% and 85.2%, respectively), compared to patients with two copies of ApoE4 (73.3% remaining stable or improving).
For more information, read the Biogen press release, here: https://investors.biogen.com/news-releases/news-release-details/two-year-real-world-study-leqembir-united-states-presented