Biogen and Eisai presented new long-term data on their Alzheimer’s treatment Leqembi at the Alzheimer’s Association International Conference. The findings showed that the drug continued to slow the progression of early-stage Alzheimer’s disease over a four-year treatment period, with no new safety issues identified.
Leqembi, which received U.S. approval in 2023, is currently administered through intravenous infusion. An injectable formulation is under review by the U.S. Food and Drug Administration (FDA), with a regulatory decision expected by August 31. Eisai’s Chief Clinical Officer Lynn Kramer said, “They have been communicating with us all the time in an expected manner.” He also stated that the injectable version “will be very helpful to starting new patients” on the treatment.
The four-year data builds on results from the pivotal trial that supported Leqembi’s initial approval. In that trial, patients with early-stage Alzheimer’s who received the drug showed a 27% slower rate of cognitive decline after 18 months compared to those given a placebo. Around 95% of the original trial participants continued in the follow-up phase. In this extended period, the drug was associated with a 34% slower decline in cognitive function compared to projections for untreated individuals with similar conditions.
Leqembi is designed to target protofibrils, which are early forms of the amyloid plaques commonly associated with Alzheimer’s disease. According to the data shared at the conference, brain swelling and bleeding linked to amyloid-removal therapies were mainly observed during the first six months of treatment, with no new safety issues reported over the longer term.
More than half of the patients who started treatment in the early stages of Alzheimer’s continued to show improvements in clinical scores after four years on the drug. The long-term findings were derived from the open-label extension phase of the Clarity AD study, which evaluated patient outcomes using the Clinical Dementia Rating scale.
Over a three-year period, patients receiving Leqembi scored 1.01 points better than the expected decline benchmarked against the Alzheimer’s Disease Neuroimaging Initiative (ADNI) cohort. By the end of the four-year follow-up, this difference had increased to 1.75 points. According to the companies, this indicates that Leqembi helped patients remain in the early stages of the disease longer than what would be expected from the natural course of Alzheimer’s.
In a tau protein substudy within Clarity AD, 69% of patients with early-stage disease showed either improvement or no decline in clinical scores after four years on Leqembi. The companies stated that the data suggest initiating and maintaining treatment with lecanemab in early-stage Alzheimer’s may provide sustained long-term benefits.
Eisai is also conducting a separate study evaluating Leqembi in individuals who have not yet shown symptoms of Alzheimer’s. That study is expected to be completed in late 2027. In parallel, Eli Lilly is investigating its Alzheimer’s candidate, Kisunla, in patients with confirmed disease pathology but no evident cognitive impairment.
Leqembi is currently the first fully approved anti-amyloid antibody treatment for Alzheimer’s disease. Eisai reported in its third-quarter results that the drug experienced 30% quarter-on-quarter growth. As of February, approximately 13,500 patients in the U.S. were receiving Leqembi, a figure that exceeded expectations cited in analyst commentary. Biogen CEO Chris Viehbacher noted during the company’s fourth-quarter earnings call that efforts are now being directed toward expanding the prescriber base.
