Alexion's stock fluctuation at Amgen's hands

Ten days ago, Alexion Pharmaceuticals traded up after a Spanish news site published an article claiming that Amgen was preparing a buyout offer. That rumored deal never happened. But on Friday, the U.S. Patent Trials Appeals Board, acting on an Amgen request, agreed to start an inter partes review of several key patents covering Alexion’s blockbuster rare disease medicine Soliris.

So, yeah, Amgen and Alexion are getting into it, just not the way investors expected. Alexion shares fell 10% on Friday, giving up all that M&A-fueled upside, and also most of the stock’s gain for the entire year.