Shares of Biogen (BIIB -2.6%) are under pressure as the company investigates the death of a patient who took the MS drug Tecfidera. "We are actively investigating," a company spokesperson tells Reuters, adding that "the patient was not on Tecfidera at the time of death." BIIB said yesterday that the patient's death was unlikely to be related to the drug. ISI analyst Mark Schoenebaum isn't worried and even reaches into his slightly-dated pop culture reference bag, telling clients to "chillax."