Eisai's 40-year effort in Alzheimer's drug discovery led to breakthroughs, including anti-amyloid and anti-tau antibodies. Early diagnosis, crucial for effective treatment, historically relied on brain autopsy. Advances in biomarkers, like amyloid PET and CSF tests, have improved diagnosis but face limitations. Blood biomarkers (BBMs) offer practical advantages, with recent studies showing plasma p-tau217 tests matching CSF accuracy. The development of BBMs and anti-amyloid therapies aims to transform AD diagnosis and treatment.