Eisai Co., Ltd. (4523.T) fair value

ACCE thesis

Eisai makes Leqembi (lecanemab), the Alzheimer's antibody it co-develops with Biogen and sells in the US, Japan and other markets, alongside its established neurology and oncology franchises including Lenvima. Its moat rests on being one of the few companies with an approved disease-modifying Alzheimer's therapy, which gives it first-mover access to a patient pool that is still largely untreated and to the diagnostic and infusion infrastructure that comes with it. The near-term driver is Leqembi's uptake curve, where the market will judge whether a subcutaneous maintenance format and expanded diagnostic capacity translate into sustained patient growth. Revenue is growing 15.6% with a 76.7% gross margin, yet operating margin is only 10.6% and ROE is 5.0%, so the investment case depends on margins widening as the launch scales rather than on the current earnings base. The trailing P/E of 36.9 compares with a forward P/E of 25.0, which implies the market is already pricing in meaningful earnings growth over the next year, so the thesis needs confidence in that ramp before it is worth a deeper look.