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While most Foolish investors are focused on long-term investing, it's also wise to stay apprised of short-term movements in stock prices, as the reasons for these moves could be relevant to investors' long-term investment theses. That said, let's look at the five best-performing stocks on the S&P 500 last week: Biogen Idec (NASDAQ: BIIB ) , Tyson Food (NYSE: TSN ) , Time Warner Cable (UNKNOWN: TWC.DL ) , Celgene (NASDAQ: CELG ) , and Gilead Sciences (NASDAQ: GILD ) .
Before we home in the reasons for these stocks' weekly jumps -- which ranged from 7.7% to 20.2% -- let's get a better perspective on their performances by moving our time lens out to one year. As this chart shows, four of the five have significantly outperformed the market all year, with Time Warner tracking the market until its recent leap. Clearly it's been a good year to be invested in big biotechs, with the three biotechs on our list -- Biogen, Gilead Science, and Celgene -- boasting the best one-year returns.
Biogen Idec: Up 20.2%
Biogen Idec received good news from the European Union's Committee for Medicinal Products for Human Use, or CHMP, on Friday relating to its multiple-sclerosis drug Tecfidera. The committee ruled Biogen's drug a "new active substance" -- meaning it can be protected from generic competition for 10 years.
Given that the European Commission -- comparable to the U.S. Food & Drug Administration -- usually follows CHMP's rulings, the European launch of the drug as a novel treatment is nearly a sure thing.
There had been uncertainty as to whether the E.U. committee would determine Tecfidera -- which launched in the United States earlier this year -- to be a novel substance. Obviously, the exclusivity means a larger global market for Biogen's Tecfidera, which is already on its way to achieving blockbuster status in the U.S.
Tyson Food: Up 10.6%
Meat processor Tyson Food's leap can be attributed to its strong fiscal fourth-quarter results, released last Monday, which also included a bump up in 2014 revenue guidance.
The $10.9 billion market-cap company -- which operates in the chicken, beef, pork, and prepared-foods segments -- posted quarterly revenue up 7% year over year to $8.9 billion and earnings up almost 23% to $0.70 per share. Revenue was in line with analysts expectations, while earnings topped the consensus estimate of $0.69.
Strong performance in its beef and chicken segments drove the results, while pork was a bit of a problem child, as Foolish writer Michael Lewis discusses in his recap of Tyson's results.
Time Warner Cable: Up 10%
Time Warner Cable's shares were driven higher by reports suggesting the company could be the object of a bidding war between Charter Communications and Comcast as the cable industry could be on the verge of of consolidation.
Time Warner, the second-largest cable company in the U.S., pairing with either company would create an 800-pound gorilla in the industry. Comcast is already the industry's top dog, while Charter Communications is the fourth-largest cable-provider in the country.
Celgene: Up 8.9%
Like Biogen, fellow big biotech Celgene also received an end-of-the-week green light from the E.U.'s CHMP. The committee recommended approving Celgene's Abraxane to treat pancreatic cancer, in combination with Eli Lilly's Gemzar.
Celgene acquired Abraxane when it bought Abraxis BioSciences in 2010. At that time, the drug was approved only as a breast cancer treatment. Celgene has since been testing it for new indications, and it received approval in the U.S. for lung cancer last year and pancreatic cancer in September.
Gilead Sciences: Up 7.7%
It seems like CHMP likes hat tricks, as Gilead Sciences marks the third biotech CHMP bestowed good news upon last week. The committee recommended approving Gilead's hepatitis C drug Sovaldi. This is an especially notable drug, as it would be the first treatment for the hepatitis C virus that eliminates the need for the injectable interferon, which has serious side effects.
Sovaldi is expected to be granted FDA approval for use in the U.S. by early December.
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