Biogen resurrects failed Alzheimer's treatment

Biogen plans to pursue FDA approval early next year of an experimental Alzheimer's drug that the company had squashed six months ago after initial signs showed the drug didn't work.

Why it matters: This is a major and unexpected development that hints at a possible Alzheimer's treatment, driving Biogen's stock price up by more than 25%. But there remains widespread skepticism about how Biogen is interpreting the clinical trial data, and whether the data shows the drug is effective.