Science news investigation: Clinical trial death raises safety concerns about promising antibody for Alzheimer’s disease

A clinical trial volunteer who received a promising antibody therapy for Alzheimer’s disease recently died from a massive brain hemorrhage associated with the drug, lecanemab, according to an unpublished case report Science has obtained. The death, the second publicly linked to the antibody, intensifies questions about lecanemab’s safety and how widely it might be prescribed if ultimately approved by regulators. The woman suffered a stroke and was treated with a clot-busting blood thinner, tissue plasminogen activator (tPA) – which immediately led to the hemorrhage. She turned out to also have cerebral amyloid angiopathy (CAA), a condition in which the smooth muscle of brain blood vessel walls is gradually replaced with amyloid deposits. Lecanemab targets amyloid and, according to CAA experts, its use likely weakened the women’s blood vessels – triggering the hemorrhage. Although it can be difficult to diagnose before death, even with brain scans, CAA occurs in about half of Alzheimer’s patients, As a result, it could be dangerous to broadly administer lecanemab without strong warnings about its apparent interaction with blood thinners, according to scientists who reviewed the details of the woman’s death.