Lecanemab is a study drug being tested to see if it can help people with early signs of Alzheimer's disease, a memory problem. The study checks if lecanemab works better than a placebo (a pill with no medicine) over four years. It also looks at how safe it is to take lecanemab for a long time.

People who want to join need to be between 55 to 80 years old. They must have a special brain test called an amyloid PET scan, which looks for amyloid, a substance linked to Alzheimer's. They need a helper, like a family member, who can talk about how they're doing. People with certain health problems or who are taking specific medications can't join.

• The study lasts for 216 weeks (about 4 years), with regular check-ups.
• Participants are required to have a helper who can stay in touch weekly.
• People who join may have risks, like side effects, and need to follow all study rules.

Participants are asked to give written permission and be willing to follow study instructions. The goal is to find out if lecanemab can help with memory issues before Alzheimer's gets worse.