) at market perform.
Analyst Mark E. Karvosky says Biogen Idec and Elan reported its first case of PML in a patient receiving monotherapy Tysabri.
He reminds investors this is third case of PML (progressive ultifocal leukoencephalopathy) overall. The other two cases occurred in patients receiving Tysabri and an Avonex combo therapy.
Karvosky says the news is clearly negative and complicates predictions about when and if Tysabri will return to the market. But his estimates for Biogen don't include any Tysabri revenue so while he expects the stock to remain volatile over the next few quarters, he would be a buyer under $36. He maintains his $42 target.