It might have something to do with CLTR , which although not near FDA approval for its competing product, has gotten a lot of publicity lately and may have the superior product.
I agree IDEC has been a victim of "Buy on rumor, sell on news", but the news is entirely too good. I expect the stock to be selling in the 50 range by mid-1998. Also it is now a "great" take-over target for the larger drug companies.