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An experimental Alzheimer's drug could be approved next year. But it comes with risks

STEVE INSKEEP, HOST:

An experimental drug is raising hope for the treatment of Alzheimer's disease, although it does come with some risks. So NPR's Jon Hamilton looked at the evidence.

JON HAMILTON, BYLINE: The drug, called lecanemab, only slows down Alzheimer's a bit. But it dominated last week's Clinical Trials on Alzheimer's Disease meeting in San Francisco. Dr. Eric Reiman was there. He's the executive director of Banner Alzheimer's Institute in Phoenix.

ERIC REIMAN: There was a feeling of elation that this was a milestone in the fight against Alzheimer's disease and very important.

HAMILTON: A study of nearly 1,800 people in the early stages of Alzheimer's found that lecanemab slowed down declines in memory and thinking by 27%. Reiman says that's a modest but meaningful benefit from the drug.

REIMAN: It had effects on a range of cognitive and functional measurements that are important to families and family caregivers. But clearly, a treatment by itself that is not going to stop the progression of the disease.

HAMILTON: Lecanemab contains antibodies designed to remove a substance called amyloid from the brain. That makes it similar to the controversial drug Aduhelm, which received a conditional approval from the Food and Drug Administration last year. The agency acted despite conflicting evidence on whether Aduhelm slows down the disease. Reiman says the results with lecanemab are much clearer.

REIMAN: I'll be surprised if it doesn't get full approval.

HAMILTON: Probably sometime next year. Both Aduhelm and lecanemab have risks, including a condition known as ARIA. Dr. Sharon Cohen, medical director of the Toronto Memory Program in Canada, says when a brain scan shows ARIA, it's a sign of either swelling or bleeding.

SHARON COHEN: This sounds very dramatic to have swelling in the brain or bleeding in the brain, and of course, nobody wants that.

HAMILTON: But Cohen says even though ARIA is common, it rarely has a big impact on patients' health.

COHEN: What we've learned over time is that a very small proportion of individuals will have symptoms, and when symptoms arise, they are usually transient, mild to moderate and resolve.

HAMILTON: In rare cases, though, patients can experience brain damage or even death. Cohen says the risks of ARIA appear to be higher in people who have very high levels of amyloid in the brain or are taking blood thinners.

COHEN: There will be patients for whom this is not a good therapy.

HAMILTON: Lecanemab and other drugs that remove amyloid have another side effect that is more mysterious. They seem to cause the brain to shrink. And that concerns Dr. Madhav Thambisetty, a neurologist at the National Institute on Aging, a part of the National Institutes of Health.

MADHAV THAMBISETTY: What is a little worrying to me is that these drugs might be worsening the degenerative process that is associated with disease progression.

HAMILTON: Alzheimer's itself causes the brain to shrink, a sign that neurons are dying. So Thambisetty, whose views are independent of the NIH, expected Alzheimer's drugs to limit shrinkage rather than accelerate it.

THAMBISETTY: It's incumbent upon drug developers and researchers to try and prove that these changes are benign and do not represent a significant adverse event.

HAMILTON: Dr. Reisa Sperling directs the Center for Alzheimer's Research and Treatment at Brigham and Women's Hospital in Boston. She says serious side effects are common in treating other diseases like cancer.

REISA SPERLING: Alzheimer's is a terrible disease, and I think many patients and their physicians will be willing to take some risk. And our work is to minimize the risk.

HAMILTON: About 2 million Alzheimer's patients in the U.S. are potential candidates for lecanemab.

Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.

Jon Hamilton is a correspondent for NPR's Science Desk. Currently he focuses on neuroscience and health risks.