Why Biogen Stock Popped as Much as 37.1% This Week

Shares of Biogen (NASDAQ: BIIB) shot up as much as 37.1% this week, according to data from S&P Global Market Intelligence. The large-cap drugmaker with a market cap of $39 billion announced that its new Alzheimer's drug it developed in a partnership with Eisai showed tremendous promise in a clinical trial. As of 12:42 p.m. ET on Friday, shares of Biogen were up 35.5% this week.

On Sept. 27, Biogen put out an official press release stating that its new drug, named lecanemab, showed promise in slowing the progress of the brain-damaging disease Alzheimer's versus a placebo in clinical trials. The drug targets a plaque that builds up in the brain and is thought to cause the disease. Patients who took lecanemab saw a reduction in this plaque by 27%, on average.