Shares of Biogen /zigman2/quotes/201531540/composite BIIB -1.58% fell about 3% in afternoon trading. The Cambridge, Mass.-based biopharmaceutical company is facing a patent challenge from Mylan for its top-selling drug, multiple sclerosis treatment Tecfidera. A hearing was held Wednesday as part of the review; Evercore ISI analyst Umer Raffat wrote that "certain statements in the judge's institution decision suggested a very tough setup for Biogen on this IPR," but the hearing "appeared to have gone better than we anticipated." Tecfidera had a 3% bump in sales to $1.12 billion in the third quarter, up from $1.09 billion in the same period a year ago. Also, on Wednesday, the National Multiple Sclerosis Society came out in opposition to the pricing for Vumerity, a newly approved MS drug developed by Biogen and Alkermes /zigman2/quotes/205084517/composite ALKS -2.06% . Biogen stock is down 9.2% for the year, while the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.48% is up about 23%.