Eisai to present five-year lecanemab data at CTAD in Boston

Eisai will present five years of lecanemab treatment data from the Clarity AD long-term study and new analyses from the real-world LEADER study at the 19th Clinical Trials on Alzheimer's Disease conference, which runs 16-19 November in Boston and online.

Eisai's program includes a dedicated LEADER symposium, five oral presentations and 19 posters. One featured oral presentation will report findings through five years of lecanemab treatment in Clarity AD, covering the 18-month core phase and the long-term extension. Eisai calls it one of the longest-term follow-up datasets reported to date for an approved anti-amyloid therapy in Alzheimer's disease. Other sessions cover real-world safety, including ARIA rates across multiple countries, and lecanemab alongside alpha-synuclein co-pathology in the Clarity AD cerebrospinal fluid substudy.

Why the real-world numbers carry weight

LEADER is a multicenter, real-world, retrospective study of lecanemab use in early Alzheimer's disease across diverse US treatment centers, three years after FDA approval. Its patients are more diverse, older and more medically complex than the 1,795 participants in Clarity AD, the Phase 3 trial that won approval in July 2023. The CTAD analyses follow a featured LEADER research session at the Alzheimer's Association International Conference in London on 14 July 2026, which was scheduled to report outcomes, intravenous once-monthly maintenance dosing, and physician and patient satisfaction.

The CTAD data arrive amid a dispute over lecanemab's benefit. Cochrane's April 2026 review covered 17 Phase 3 trials and more than 20,000 participants treated with amyloid-targeting antibodies. It concluded that absolute effects on cognitive decline and dementia severity were "nonexistent or negligible". The UK Dementia Research Institute called the methodology "fundamentally flawed".

The institute argued the review pooled 15 largely failed or withdrawn drugs with lecanemab and donanemab. Eisai responded that long-term data out to four years and real-world experience with tens of thousands of patients globally show benefit. LEADER tracks patients in routine care, evidence the Cochrane review of Phase 3 trials did not cover. The CTAD analyses will report real-world outcomes, safety including ARIA rates, and treatment persistence.

The delivery question behind the data

Eisai also won US approval on 13 July 2026 for Leqembi Iqlik, a once-weekly subcutaneous starting dose of 500 mg, given as two 250 mg injections of about 15 seconds each, with a launch planned for late August 2026.

Subcutaneous maintenance, approved in August 2025, is 360 mg once weekly once 18 months of intravenous or subcutaneous treatment is complete. Substudies in the Clarity AD long-term extension showed once-weekly subcutaneous dosing reached exposure equivalent to intravenous dosing, with ARIA-E rates expected to be comparable. The LEADER symposium includes an analysis of at-home subcutaneous administration, the delivery route Leqembi Iqlik introduced.

What happens next

The LEADER symposium is scheduled for Wednesday 18 November, 11:00-11:40 AM ET. Eisai's 29 October announcement gave no results, so effect sizes, ARIA rates and treatment persistence from the new analyses remain unknown.