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While the S&P 500 has traded sideways since the start of the year, biotech stocks have once again managed to show that they are the place to be, posting double-digit gains since the start of the year. The SPDR S&P Biotech ETF (NYSEMKT:XBI), which holds over 100 biotech stocks, is up more than 24% year to date, which simply blows away the returns of the overall market.

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Despite the huge run, our contributors think there are plenty of names in the biotech universe that could still be considered a good buy right now, so we asked them so share a biotech stock that they think might be worthy of consideration. Read on to see what they had to say.

Todd Campbell: The FDA is set to make a decision on whether to approve AstraZeneca's (NYSE:AZN) gout medication lesinurad on Dec. 29, and there's a lot of uncertainty that could cause shares to pop or drop.

In October, a key advisory committee voted 10-to-4 that the FDA should approve lesinurad, but the committee was nearly split when it voted 7-to-6 (with one abstention) on the drug's safety.

The committee's concerns stem from cases of major cardiac events and death in gout patients receiving a 400 mg dose of lesinurad, and those concerns could cause the FDA to reject the drug until more advanced safety data is collected, or it could approve the drug with a black-box warning of the drug's risks.

If lesinurad is approved, it could bring in hundreds of millions of dollars in annual sales for AstraZeneca, but if it's not, then AstraZeneca's $1.2 billion purchase of lesinurad's drug developer Ardea Biosciences in 2012 will have been a flop.

According to AstraZeneca, as many as 2 million gout patients are inadequately being treated with existing gout medications.

Because this FDA decision could be a binary event, investors will want to approach AstraZeneca cautiously. But since the advisory committee did vote in the drug's favor and the FDA usually follows committee recommendations, and the market may not fully appreciate an approval, it may be worth nibbling on AstraZeneca stock in December.

Brian Feroldi: One name that continues to impress me is Vertex Pharmaceuticals (NASDAQ:VRTX). Vertex has been a winner for a long time, having smoked the market over the past one, five, and 10 years, but I think there are plenty of reasons to believe the good times will continue to roll.

First off, the company now boasts two successful drugs on the market that treat cystic fibrosis, Kalydeco and newly launched Orkambi. Kalydeco has been growing strong since its launch in 2012, as sales were up 31% in the most recent quarter, and Vertex believes the drug will produce sales of at least $605 million for the year. Growth should continue well into next year, too, as Kalydeco just got two more label expansions in Europe that should grow its worldwide addressable market by roughly 13%. The company is also slated to hear in February from the FDA about yet another label expansion opportunity, which if approved would further grow its market by another 35% or so.

On top of that growth is Orkambi, which just received regulatory clearance in the U.S. in July. Sales last quarter came in at $130 million, which is a heck of a good start for the drug, especially when considering it's likely to get the green light in Europe in the next few months.

With both Orkambi and Kalydeco firmly in growth mode, Wall Street sees Vertex posting revenue of $2.48 billion next year, which should finally allow the company to turn a profit. Given that it also has another cystic fibrosis treatment, VX-661, in phase 3 trials and it recently made a hefty equity investment in a gene editing company, Vertex is fast turning into a financial powerhouse, and I think it's a great biotech stock to buy in December.

Sean Williams: To be clear, I'm in no way suggesting investors time their purchases, because that's about a successful as a coin flip, but I'd urge biotech-savvy investors to give Alexion Pharmaceuticals (NASDAQ:ALXN) a closer look. 

The biggest knock against Alexion – other than the nearly $537,000 annual wholesale cost for Soliris, which makes the company a prime target for prescription-drug reform – is that its product portfolio has been entirely reliant on Soliris up until this point. Soliris, which treats two rare diseases -- paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome -- has been growing like wildfire. However, there's always concern that being over-reliant on a single therapy could come back to haunt a drug developer. 

Enter Strensiq and Kanuma. Strensiq was recently approved in the U.S. and EU as a treatment for hypophosphatasia, and Kanuma was given the green light in the EU to treat lysosomal acid lipase deficiency. In other words, Alexion's product portfolio is beginning to diversify. 

In September, the Food and Drug Administration delayed its PDUFA decision on Kanuma in the U.S. to Dec. 8, despite bestowing a breakthrough designation on the drug during its development. The interesting point about the delay is that the regulatory body asked for additional chemistry, manufacturing, and control information, and not additional clinical data. While no given, this could imply that an approval is looking likely. 

With peak annual sales projected to be around $1 billion by 2021, Kanuma could quickly boost profits for Alexion. 

Brian Feroldi has no position in any stocks mentioned. Sean Williams has no position in any stocks mentioned. Todd Campbell has no position in any stocks mentioned. The Motley Fool recommends Vertex Pharmaceuticals. 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.