The study is checking if a new drug, **lecanemab**, helps people with early signs of Alzheimer's, a brain disease causing memory loss. They want to see if lecanemab is better than a placebo, which is a fake treatment with no real medicine, in improving memory and reducing amyloid, a protein that affects the brain, over 216 weeks (around 4 years).

• **Study Length**: The study lasts 4 years with regular check-ups.
• **Eligibility**: Participants must be 55-80 years old, with specific brain test results, and have someone to help them with the study.
• **Risks and Tests**: Participants shouldn't have certain health issues and will undergo regular brain scans and tests.

Lecanemab is tested for long-term safety. Participants agree to follow the study rules and have a partner who can report on their daily activities. If you've had severe health problems or take certain drugs, you might not join. Pregnant women and those with risky health conditions are also excluded. The study aims to find a safe way to slow down Alzheimer's progression.