Shares of Biogen Inc. /zigman2/quotes/201531540/composite BIIB +2.19% rocketed 19% in trading on Wednesday after the Patent Trial and Appeal Board ruled in its favor on a patent challenge brought by Mylan Inc. /zigman2/quotes/209413137/composite MYL -1.04% for its blockbuster multiple sclerosis drug Tecfidera. Mylan's stock is up 2%. Tecfidera is Biogen's top-selling drug, bringing in $4.4 billion in revenue in 2019. The jump in shares on Wednesday "is because of how much of an overhang this news item has been," Mizuho Securities' Salim Syed wrote in a note. "It provides an entry point perhaps for any aducanumab bulls waiting on the sidelines for this event to pass." Aducanumab is Biogen's investigational Alzheimer's disease treatment. Biogen's stock has gained 15% over the past three months, while the Health Care Select Sector SPDR Fund /zigman2/quotes/205918244/composite XLV +1.21% , an exchange-traded fund, is up 7%.