Eisai And Biogen Say Four Years Of Leqembi Helps In Slowing Down Alzheimer's Disease Progression

Eisai Co., Ltd. and Biogen Inc. (BIIB) announced positive long-term data from their Phase 3 Clarity AD study, demonstrating that continuous treatment with Leqembi significantly slowed progression in patients with early Alzheimer's disease. The study showed a clinical decline slowed by 1.75 points, with 478 patients still receiving the drug after four years in the open-label extension. These results, presented at AAIC 2025, underscore Leqembi's sustained efficacy and potential as a long-term therapeutic option for Alzheimer's.

Analysis

Biogen Inc. (BIIB) and its partner Eisai have presented significant long-term data from the Phase 3 Clarity AD study, reinforcing the efficacy of their Alzheimer's drug, Leqembi. The results, unveiled at the Alzheimer's Association International Conference, demonstrate that continuous treatment slowed clinical decline by a notable 1.75 points in patients with early Alzheimer's. The high patient retention rate in the open-label extension study is a particularly strong signal; 95% of the 1,795 core study participants continued, with 478 patients remaining on treatment for four years. This high continuation rate suggests a favorable real-world risk-benefit perception by patients and clinicians, which is critical for long-term commercial success. The positive data strengthens Leqembi's profile as a foundational treatment, underpinning its potential for a sustained revenue stream and bolstering Biogen's fundamental outlook in the competitive Alzheimer's market.

Key Decisions for Investors

• Given the positive long-term efficacy and strong patient retention data, investors should view these findings as a significant de-risking event for Leqembi's commercial trajectory, supporting a bullish outlook on Biogen (BIIB).
• Monitor Leqembi's upcoming quarterly sales figures and prescription trends closely, as these will be the primary indicators of a successful translation from clinical efficacy to commercial revenue.
• Consider the sustained patient use demonstrated in the study as a key factor for long-term revenue modeling, as it suggests a durable patient base and reduced churn compared to therapies with less compelling long-term data.