Two major winners stood out in the market from the biotech space today. Alexion Pharmaceuticals (NASDAQ:ALXN) delivered strong quarterly results that saw the stock shoot up by more than 20%. The company's Q4 sales surged 38%, to beat analyst estimates, as its drug Soliris continues to grow in Western Europe, Japan, and in the U.S., and its adjusted net income climbed 45%. The real story with this stock, however, is that it has moved to the low tax haven of Ireland, cutting its tax rate down to the 15% range. And with sales of Soliris strong, this tax break will translate to bottom-line growth in a very meaningful way.

Meanwhile, today's staggeringly explosive winner was Dicerna Pharmaceuticals (NASDAQ:DRNA), which IPO'd today, and saw an unbelievable 170% pop. The company is an RNA interference technology platform, and in this video, Motley Fool health-care analyst David Williamson calls it an excellent example of the biotech bubble at the moment. When David sees a biotech -- with a pipeline that contains nothing at a later trial stage than phase 1 -- experiencing such a skyrocketing jump upwards, he sees it as a clear sign of market overenthusiasm. He warns investors that if they didn't get in at the IPO price, they should stay away until Dicerna shows some meaningful clinical data.