If the market was confident in the CF franchise - it is not because the botched the data and are not showing any improvement in sweat chloride. All speculation at this point... and that's the difference between the $20 this is worth and the $38 it is right now.... considering that this was just recently $60 in September.... that is a real strong indicator of where this is going to continue to go.
There are commonly accepted probabilities for success used to value pharma pipelines... those probabilities as they are make this a 5.5 billion dollar company. If you fudge with the probabilities, clearly the value goes up.
So it is clear to me that the market has completely discounted all the negative news and has already priced in hype for the CF franchise. This is a ripe candidate then for any news to sell off.... which it has been successfully doing for the last three months.