Biogen shares drop after report of death of patient while on Tecfidera

Biogen Idec's shares were down 5 percent as of 2 p.m. after company executives disclosed that a patient who had taken its blockbuster multiple sclerosis pill Tecfidera for more than four years was diagnosed with a rare brain infection and died, although they said the death was not due to the drug.

Executives on a conference call this morning said immediate cause of death was pnemonia, but the fact that the patient was also diagnosed with progressive multifocal leukoencephalopathy, or PML, may be behind the selloff. That's the same infection that caused another of Biogen's MS drugs, Tysabri, to be withdrawn from the market in 2005 after three patients in a clinical trial died. Tysabri was reintroduced the following year and remains on the market as one of the company's top sellers.

Ever since Tecfidera's launch in March 2013, it has been considered the Cambridge company's biggest potential moneymaker for the coming several years. For the three months that ended in September, Tecfidera brought in more revenue than any of the dozen or so other drugs Biogen sells, nearly a third of its total for the quarter. The drug also carries a warning for lymphopenia (abnormally low white blood cells), according to Biogen CEO George Scangos, which is a known risk factor for PML.

"This patient did have severe lymphopenia for three and a half years, and we believe the length of time on Tecfidera is not the issue. The issue is related to lymphopenia," Scangos said on the conference call."Despite this tragic loss, we believe the risk profile of Tecfidera remains unchanged."

Scangos said the company has reported the death to the FDA and is working with the agency to determine whether the labeling for Tecfidera needs to be changed as a result.