ABOVE: Neurons with amyloid plaques accumulating on their axons © ISTOCK.COM, SELVANEGRA

Update (November 30): The data described in Biogen and Esai's announcement was published in The New England Journal of Medicine Tuesday (November 29). Alongside the effect of slowing cognitive decline in some Alzheimer's patients, the paper shows that lecanemab may come with an increased risk of brain swelling and bleeding, The New York Times reports.

Update (November 28): A 65-year-old woman participating in a clinical trial for lecanemab died from a severe brain hemorrhage shortly after she was treated with the drug, Science reports. This is the second fatal brain hemorrhage among participants in the lecanemab trial, raising suspicions that the drug may interact dangerously with blood-thinning medications. In response, lecanemab’s manufacturer Eisai declined to comment on the specific cases, telling Science 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.”

Pharmaceutical companies Biogen and Eisai announced yesterday (September 27) that their new Alzheimer’s disease drug, called lecanemab, slowed the rate of cognitive decline in patients by 27 percent compared to a placebo during a phase 3 clinical trial that involved 1,795 participants and lasted 18 months.

“It’s not a huge effect, but it’s a positive effect,” Ronald Petersen, director of the Alzheimer’s Disease Research Center at the Mayo Clinic, who didn’t work on the drug, tells Reuters.

The New York Times reports that the trial included participants with either mild dementia (often a precursor to Alzheimer’s) or early-stage Alzheimer’s disease. That makes it the largest study to date intended to determine whether clearing the brain of amyloid plaques, a feature of Alzheimer’s, slows the progression of the disease, according to the Times. The results have not yet been peer-reviewed.

Eisai chairman and chief executive Ivan Cheung told reporters at a Tuesday press briefing that this was “the first definitively positive large clinical trial to show that you can indeed slow down Alzheimer’s disease at this very early symptomatic stage,” according to the Times.

Both Eisai and Biogen are already pursuing accelerated FDA approval for the drug, according to The Washington Post. Eisai announced today that it will also seek full FDA approval, which the Post reports would make it more likely that Medicare and other insurers would cover the drug.

See “Lawmakers Request Information About Alzheimer’s Drug Approval

Lecanemab follows on the heels of Aduhelm, another Alzheimer’s drug developed by Biogen and Eisai, which also targets amyloid plaques in the brain but has largely been considered a failure following its controversial FDA approval, the Associated Press reports, due to weak and conflicting clinical data and many insurers declining to foot the bill of $56,000 per year for treatments. Though experts who spoke to the Times and the Post expressed caution about making predictions based on preliminary results, they generally expect lecanemab to fare better than Aduhelm did.

“A 27 percent slowing of deterioration seems like a modest effect, but for patients with Alzheimer’s, this could be very meaningful,” University of California, San Francisco, neurologist Gil Rabinovici, who wasn’t involved in the drug’s development, tells the Post.

See “The Hunt for a Blood Test for Alzheimer’s Disease