An experimental Alzheimer’s drug has shown encouraging results in a clinical trial, exciting medical professionals who have struggled for decades to find an effective treatment. At the same time, some researchers hypothesize that the deaths of two trial participants are tied to the drug, called lecanemab.
In a clinical trial of 1,795 participants with mild Alzheimer’s or cognitive impairment, lecanemab appeared to slow cognitive decline. Researchers announced their preliminary, promising findings in September, and they published the trial’s full results Tuesday in the New England Journal of Medicine. Participants who received the drug experienced 27 percent less cognitive decline than those who received the placebo.
The first reported death that may be linked to lecanemab occurred in June, Stat News’ Jason Mast wrote in October. An investigator concluded the death was connected to the drug, since it came after the participant, who was in his late 80s and was taking a blood thinner, had bleeding in his brain.
The second fatality was a 65-year-old woman who received the drug during the trial, reports Science’s Charles Piller, who obtained an unpublished case report on the death. After suffering a stroke, she was given a common blood thinner. She then experienced substantial bleeding in her brain and died a few days later.
“[Regulators] should take this case report seriously into account, because we’re talking about significant side effects,” Andreas Charidimou, a Boston University neuroscientist who looked at the case report for Science, tells the publication.
In 2020, about 5.8 million Americans had Alzheimer’s, a disease of progressive cognitive decline, according to the Centers for Disease Control and Prevention (CDC). By 2060, the CDC estimates the number of people with the disease will triple. Alzheimer’s is the seventh leading cause of death in the United States, and there is currently no cure.
Scientists don’t fully understand what causes Alzheimer’s. But it is thought the buildup of proteins, such as amyloid plaques and tau tangles, causes damage in the brain. Lecanemab is meant to break down amyloid before it accumulates, which could slow the progression of Alzheimer’s.
However, lecanemab can inflame and weaken blood vessels, according to Science. Twenty percent of study participants receiving the experimental treatment showed signs of swelling or bleeding in brain scans, though less than 3 percent experienced symptoms, Nature News' McKenzie Prillaman wrote in September.
Bleeding is also a common side effect of blood thinners. The death of the first participant highlights the risk for patients on blood thinners receiving the drug, Stat News writes. The second participant received a blood thinner after her stroke that can sometimes cause brain bleeds, per Science.
James Nicoll, a neuropathologist at the University of Southampton in England and a consultant for Biogen, one of the drugmakers, tells Science that if the drug were approved, mixing lecanemab and blood thinners is “something you would want to keep a close eye on.”
The other drugmaker, Eisai, told the publication in a statement that “all the available safety information indicates that lecanemab therapy is not associated with an increased risk of death overall or from any specific cause.”
A spokesperson for Eisai told Stat News after the first death that “there’s no reason to believe that lecanemab contributes to death overall in the study, or by any specific cause.” But the publication obtained documents in which the company wrote there was “at least a reasonable possibility” the drug contributed.
The Food and Drug Administration is expected to announce whether they will approve the drug in January.