Biotech has had yet another stellar year in 2013 with the SPDR S&P Biotech ETF (NYSEMKT:XBI) up more than 40% year to date. With that in mind, here's a look at the four top performers in the sector this year.

ACADIA takes first
ACADIA Pharmaceuticals (NASDAQ:ACAD) is up more than 400% this year and is easily the biggest winner in the sector. Acadia's monstrous growth story centers around its experimental Parkinson's disease psychosis drug pimavanserin. The drug is presently in the throes of final supportive studies required by the U.S. Food and Drug Administration, or FDA, for a New Drug Application, or NDA, to be filed late next year.

The company is also evaluating the drug in two mid-stage trials for Alzheimer's disease psychosis and schizophrenia. Nonetheless, I think Acadia's amazing run has finally topped out, and it may end up losing its top spot before year's end.

Puma takes Place but is climbing
Puma Biotechnology (NYSE:PBYI) is this year's biotech runner-up with its princely 356% gain. Even so, Puma may end up overtaking Acadia for the top spot based on the stunning performance of its shares in recent days.

Puma's triple-bagger story largely revolves around the company's strong mid-stage results for its breast cancer drug neratinib. Specifically, Puma announced that patients receiving neratinib had a higher pathological complete response rate than the current standard neoadjuvant chemotherapy. And a simulation analysis showed that the drug was highly likely to succeed in a late-stage trial.

That's reassuring because late-stage trials are where promising oncology drugs typically go to die. Indeed, I suspect that's why Puma performed a simulation analysis in the first place. Looking ahead, Puma is also evaluating neratinib as a treatment in a number of other cancers, with a handful of data read outs expected next year. In sum, Puma looks like it will continue to climb into the New Year and beyond.

Celldex takes the show
Celldex Therapeutics (NASDAQ:CLDX) looks like it will take show after its hefty 270% gain. Celldex shares have been on a tear the past couple of years due to the strong trial results for the company's brain cancer drug rindopepimut, as well as its breast cancer drug CDX-011. Rindeopepimut is currently in advanced clinical testing for glioblastoma multiforme, a particularly aggressive and deadly form of brain cancer.

CDX-011 is about to enter a pivotal registration trial where the drug's effectiveness at treating triple negative breast cancer patients will be tested against the current standard treatment capecitabine. Celldex also has a host of early stage clinical candidates, giving the company a fairly robust pipeline.

To pay for all these clinical trials, Celldex is introducing 7 million new shares of common stock that will raise approximately $162 million in proceeds. In a rare turn of events, however, the market immediately shrugged off the offering, and actually drove share prices higher. Even so, Celldex does have a stately market cap exceeding $2 billion, which is pricey for a developmental stage biotech. As such, Celldex's furious rise is likely to be tapering off.

Honorable mention goes to Alnylam or does it?
Alnylam Pharmaceuticals (NASDAQ:ALNY) comes in fourth after rising more than 220% this year. This developmental stage biotech earns honorable mention largely because of receiving fast-track status from the FDA for its late-stage drug candidate patisiran, as a possible treatment for transthyretin-familial amyloid polyneuropathy. In plain English, the drug is targeted as a treatment for a rare, inherited neurodegenerative disease. Patisiran is being co-developed with partner Sanofi, which recently paid Alnylam $7 million for the drug's success at the mid-stage level.

Although the company has a host of clinical candidates, Alnylam does not have a commercially available drug, and relies heavily upon partnerships for its revenue. Consequently, I think the company's market cap of almost $4 billion leaves little room for growth at this point. Nevertheless, Alnylam shares keep on edging higher, thus challenging Celldex for third place.

George Budwell has no position in any stocks mentioned. The Motley Fool recommends Alnylam 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.