Reporting on Alzheimer’s disease over past few decades has been both rewarding and heartbreaking. Hope for new treatments is often followed by disappointment when drugs don’t help patients as much as experts had hoped.

But the latest glimmer of hope is getting major headlines today. The Japanese company Eisai reported at a conference last night that its drug lecanemab helped people with mild-to-moderate Alzheimer’s disease slow their cognitive decline by 27% compared to people who took a placebo. Even better, the effect increased over time.

It's not an enormous improvement, but it's better than anything currently available. Here are the three most important things to know:

• Lecanemab works by targeting amyloid, a protein that builds up in the brain during Alzheimer’s and eventually damages neurons. Other amyloid-based drugs—including the only approved treatment for the disease, aducanumab (or Aduhelm)—haven't been very effective. At the same conference, Roche reported that its anti-amyloid compound did not reduce amyloid enough to slow down progression of Alzheimer’s to a significant extent.
• The drug comes with potential side effects, including inflammation in the brain and bleeding for those also taking anticoagulant drugs. Doctors say the inflammation is manageable if patients are monitored carefully and that the bleeding risk needs further study.
• Eisai has filed for accelerated approval of the drug, and the U.S. Food and Drug Administration is expected to make a decision by early January.

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