The Ratings Game: Biogen’s key Alzheimer’s disease drug is facing potential signs of trouble

Biogen Inc.’s crucial Alzheimer’s disease drug aducanumab is still a year or two from releasing key clinical trial results, but the company’s latest news may leave some investors feeling more circumspect.

Because the company saw “more variability on the primary endpoint than assumed,” Biogen BIIB, -2.51% decided to increase the sample size of two ongoing trials by about 255 patients each, Chief Medical Officer Alfred Sandrock said at a Leerink Partners conference on Wednesday.

The change, done to maintain 90% statistical power for the study, won’t affect the study’s blinded nature, which refers to how neither patients nor doctors know which is the drug and which is the placebo, Sandrock said.

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