Not really(for the most part)-
just a complex of offsetting forces and factors that elude the casual observer.
However, high frequency trading has added a dimension of arbitrary risk that is(on balance) negative for the entire market, and should be severely limited.
In simplest terms, too many people have too great a long term profit in Ariad that will, in all likelihood, start to be taxed at a rate 60% greater than the current one in 2013.
Apart from my love affair with this stock, I can't(sadly)give you a good reason why I didn't sell myself.