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.

David Williamson has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.