A phase 3 clinical trial evaluated lecanemab, a monoclonal antibody targeting amyloid-beta (Aβ) protofibrils, in patients with early Alzheimer's disease. The study involved 1795 participants aged 50-90 years with mild cognitive impairment or mild Alzheimer's dementia, confirmed by PET or CSF testing. Participants were randomly assigned to receive lecanemab (10 mg/kg every 2 weeks) or placebo. The primary endpoint was the change in the Clinical Dementia Rating–Sum of Boxes (CDR-SB) score at 18 months, with lecanemab showing a smaller decline (1.21) compared to placebo (1.66). Secondary endpoints included reduced amyloid burden on PET, improved cognitive scores, and better functional outcomes. Lecanemab reduced amyloid burden by 59.1 centiloids compared to placebo. It also showed improvements in cognitive and functional measures, though it was associated with adverse events, including infusion-related reactions and amyloid-related imaging abnormalities (ARIA). The trial found that lecanemab reduced markers of amyloid in early Alzheimer's disease and resulted in moderately less decline in cognition and function than placebo at 18 months. However, it was associated with adverse events. Longer trials are needed to assess its long-term efficacy and safety. The study was funded by Eisai and Biogen. The results suggest that lecanemab may be beneficial in early Alzheimer's disease, but further research is required to confirm its long-term benefits and safety profile.A phase 3 clinical trial evaluated lecanemab, a monoclonal antibody targeting amyloid-beta (Aβ) protofibrils, in patients with early Alzheimer's disease. The study involved 1795 participants aged 50-90 years with mild cognitive impairment or mild Alzheimer's dementia, confirmed by PET or CSF testing. Participants were randomly assigned to receive lecanemab (10 mg/kg every 2 weeks) or placebo. The primary endpoint was the change in the Clinical Dementia Rating–Sum of Boxes (CDR-SB) score at 18 months, with lecanemab showing a smaller decline (1.21) compared to placebo (1.66). Secondary endpoints included reduced amyloid burden on PET, improved cognitive scores, and better functional outcomes. Lecanemab reduced amyloid burden by 59.1 centiloids compared to placebo. It also showed improvements in cognitive and functional measures, though it was associated with adverse events, including infusion-related reactions and amyloid-related imaging abnormalities (ARIA). The trial found that lecanemab reduced markers of amyloid in early Alzheimer's disease and resulted in moderately less decline in cognition and function than placebo at 18 months. However, it was associated with adverse events. Longer trials are needed to assess its long-term efficacy and safety. The study was funded by Eisai and Biogen. The results suggest that lecanemab may be beneficial in early Alzheimer's disease, but further research is required to confirm its long-term benefits and safety profile.