TOKYO and CAMBRIDGE, Mass., Dec. 2, 2025 — Eisai Co., Ltd., headquartered in Tokyo with Haruo Naito as CEO (referred to as “Eisai”), and Biogen Inc., with corporate headquarters in Cambridge, Massachusetts, Christopher A. Viehbacher as CEO, and Nasdaq listing BIIB (referred to as “Biogen”), today jointly announced that recent findings substantiate the pharmacological action of lecanemab (its generic name, known in the U.S. as LEQEMBI®), an antibody that targets anti-Aβ protofibrils*, regarding Aβ …