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Biogen and Eisai say their second Alzheimer’s drug slows the disease in large study

The results set the stage for potential approval of the drug next year.

Hugh Courtney, who suffers from mild cognitive impairment, received an infusion of Biogen's experimental Alzheimer's drug lecanemab at McLean Hospital in Belmont.Lane Turner/Globe Staff

Biogen and its partner Eisai said Tuesday night that their experimental Alzheimer’s disease therapy successfully slowed the memory-robbing condition in a large clinical trial. The results set the stage for potential approval of the drug next year.

Although far from a cure, the therapy provides tentative hope to the millions of Americans afflicted by the devastating disease. It also offers the beleaguered Cambridge biotech firm a second chance at cracking open a multibillion-dollar drug market after doctors, hospitals, and insurers rejected the firm’s previous Alzheimer’s drug, Aduhelm.

In an 18-month study of nearly 1,800 people with mild cognitive impairment or mild dementia, the drug, called lecanemab, slowed a common measure of cognitive decline by 27 percent compared with a placebo. That result suggests the drug may be slightly better than Aduhelm.


Dr. Brent Forester, chief of geriatric psychiatry at McLean Hospital and a principal investigator in the lecanemab trial at his hospital, said he felt “cautious optimism” after reading Biogen’s summary.

“This is the first Phase 3 trial that made it all the way to 18 months and demonstrated a slowing of decline in cognitive function,” said Forester, whose hospital had two patients in the trial. He said it remains to be seen, however, whether the drug will make a meaningful difference in the lives of patients and their families.

Lecanemab doesn’t reverse or halt the disease. Its effect boils down to just half a point on an 18-point scale. But the results exceeded expectations for statistical significance, suggesting that even if the benefits are modest, they may indeed be real.

Nonetheless, there’s sure to be skepticism about the drug, given the long history of unsuccessful treatments for the disease, which has tantalized the pharmaceutical industry for decades. The negative reception to Aduhelm, the benefits of which were fiercely debated by neurologists, suggests that Biogen and Eisai may have a heavy lift ahead.


Lecanemab, which was administered as an hourlong infusion every two weeks, was not without risk. About one in five people who got the drug developed abnormalities in their brain scans that can indicate potential brain bleeding or swelling, although only a small fraction experienced symptoms. Nearly twice as many people had similar abnormalities in studies of Biogen’s previous Alzheimer’s drug, Aduhelm.

Eisai, the Japanese drugmaker that led the trial, did not offer many additional details about the data but said that it plans to publish the results in a medical journal and provide additional details at a scientific conference in late November.

A pedestrian walks past Biogen Inc. headquarters in Cambridge, Massachusetts, U.S., on Monday, June 7, 2021. Adam Glanzman/Bloomberg

Lecanemab is designed to clean up small piles of sticky proteins called amyloid, which accumulate in the brains of people with Alzheimer’s disease. For decades, neuroscientists have hoped that amyloid-busting drugs could provide a long-awaited cure for the disease.

So far that hope hasn’t panned out, as many such drugs have failed in clinical studies. But Biogen and Eisai are positioning the lecanemab results as the long-awaited confirmation of the so-called amyloid hypothesis.

“Importantly, the study shows that removal of aggregated amyloid beta in the brain is associated with a slowing of disease in patients at the early stage of the disease,” Biogen chief executive Michel Vounatsos said in a press statement.

The Food and Drug Administration could grant lecanemab an accelerated approval as early as January. Biogen and Eisai also plan to submit the drug for full approval by the end of March.


Brian Skorney, an analyst at the investment bank Baird said the results of the lecanemab trial were better than he had expected.

“It seems like a hit on the primary endpoint and a hit on all the secondary endpoints,” he said of the goals the drug-making partners had set for the late-stage trial. “I think that people will debate the magnitude [of the slowing in cognitive decline] but I think it validates targeting plaques for a treatment.”

He said it’s possible lecanemab’s slowing of decline would continue in patients who take it for more than 18 months, making the benefits more obvious.

Biogen’s future hinges on lecanemab’s commercial success or failure. If lecanemab is approved, Biogen would need to rebuild the Alzheimer’s sales division that it dismantled in the wake of Aduhelm’s failed rollout. Successful commercialization of lecanemab could easily earn Biogen billions in profits.

But if regulators, payers, or patients reject the drug, then the firm will lose its biggest chance to recoup slowly dwindling sales of its core neurological disease drugs.

Biogen and Eisai will share profits or losses on the drug, so approval and successful commercialization of the drug would be a boon to both companies. Biogen’s stock has fallen 50 percent and Eisai’s stock has fallen 63 percent since the approval of Aduhelm in June 2021.

Ryan Cross can be reached at ryan.cross@globe.com. Follow him on Twitter @RLCscienceboss. Jonathan Saltzman can be reached at jonathan.saltzman@globe.com.