Lecanemab is a humanized IgG1 monoclonal antibody that binds to some forms of amyloid. In this study approximately 1,800 participants age 50-90 with dementia and imaging evidence of amyloid deposits were randomized to biweekly IV lecanemab or placebo. After 18 months, the lecanemab group showed reductions in brain amyloid and moderately less decline on measures of cognition and function.