They are reviewing the need to declare on their labeling, the increased risk factor .... based on number of infusions, as per on their October, 3rd quarter Conference Call.

"Biogen Idec and our partner Elan currently believe, as the recent FDA update indicated, that the risk of developing PML increases with the number of TYSABRI infusions received. ...."

"We have proposed, and are currently discussing with the regulatory authorities, a potential label change to reflect this increased risk of PML with increased duration of TYSABRI exposure."

From the Q & A:

"QUESTION: May-Kin Ho - Goldman Sachs

Will you have to spell out what the risks are at different time periods?

ANSWER: Al Sandrock, MD

We are still in discussions with the regulators at this point."

"QUESTION: Steven Harr - Morgan Stanley

I wanted to get an understanding, previously you guys have said that you did not believe that TYSABRI PML risk was related to time on the drug and then clearly something changed. You gave us exposure numbers, is there something new on number of PML cases you can offer us, or is there something you can offer us as an explanation as to why you saw more patients exposed to the drug during the quarter than on therapy? It must have been 1,300 patients that dropped off during the course of the quarter.

ANSWER: Bob Hamm

You know we are not giving out actual patient numbers, but I can tell you as time goes on the numbers of patients treated for the longer duration is increased and our 95% competence intervals on the incident rate narrows and as that happens we get more clarity about the risk. That was the reason why we had decided to update the label with this increase in the risk with the length of exposure."

They also brought up the JC testing they are working on:

"Additionally, we continue to allocate significant time and resources to identifying PML risk factors and in developing ways to stratify, mitigate, and manage the risks. We are working on this internally and we are also working to set up a consortium of other interested collaborators. The premise of our work is that PML in TYSABRI treated patients' results from a convergence of factors including the presence of JC virus, immune compromise, viral mutations, duration of treatment, and perhaps other factors such as risk [oleal] MFO.

With respect to the presence of virus recent published data in larger cohorts using more refined serological techniques indicates that seroprevalence is in fact less frequent in the textbook dogma of 80% or 90%. We have analytically validated a serological method with the goal of one day offering a commercially available assay that may inform about the relative risk of developing PML."

http://seekingalpha.com/article/1676...ngs-call-trans...

10 cases in a month is a lot, even if there are 46,000 on the drug right now, and 13-odd thousand who've been on for more than 24 months. If every month 10 people continued to be added to the total, it would not be good!!.
Cherie