from
Tysabri could affect its sales growth, and that prospect weighed
on shares of Biogen and Elan
on Friday. Shares of Cambridge, Mass.-based Biogen recently fell 5.8% to $44.49, while the American depository receipts of Dublin-based Elan plunged 20% to $5.17.
Biogen spokeswoman Naomi Aoki said the incidents of PML remain rare, reiterating the company's contention that the rate remains within the 1-in-1,000 patient level implied by its label.
As of Sept.