CHICAGO—Eisai Co. and Biogen Inc. revealed new data showing their closely watched experimental drug slowed the worsening of Alzheimer’s disease, but some experts who saw the latest results said more testing is needed to validate whether the drug is truly providing a benefit.
Eisai and Biogen said in early July that the drug, known as BAN2401, showed positive results in the mid-stage study but offered few details at the time. The news sent shares of both companies soaring on hopes that the industry may finally have found a...