Affymax (Nasdaq: AFFY) is up about 20% today after the Food and Drug Administration released documents ahead of the advisory panel meeting on Wednesday to review its anemia drug, peginesatide. But this isn't one of those times when the documents let you know definitively which way the FDA is headed.

Not even close.

Let's call it going from completely uncertain which way the panel will vote, to having some confidence that it's not a complete negative. There was some possibility that the FDA would be hypercritical of peginesatide. The jump today is an indication that investors are sighing in relief.

But Affymax is still only a $225 million company even after today's increase. There's plenty of upside if the FDA approves peginesatide, because it isn't clear that it will.

There weren't any surprises in the documents made available for the panel members, but peginesatide isn't without problems. The drug treats dialysis patients as well as other anemia drugs -- Amgen's (Nasdaq: AMGN) Epogen and Aranesp, and Johnson & Johnson's (NYSE: JNJ) Procrit. But there was a safety concern in one of the trials testing peginesatide in patients not on dialysis.

Affymax and its partner, Takeda, aren't seeking an approval for patients not on dialysis, but the poorer cardiovascular outcomes can't be ignored. They're either real and just not seen in the trial of dialysis patients, or they're just an artifact of the non-dialysis trial. You can make arguments either way, but as far as I can tell, the only way to prove it definitively one way or the other would be to run a large trial.

The panel of outside experts only has an advisory vote, but I'd expect the panel's opinion to be influential on the agency, given the inconsistent data. If this was a high unmet need, I could see the panel ignoring the other trial. But with other drugs on the market, the panel is likely to give it some weight.

The question is just how much.

My guess is the panel recommends against the drug or offers up a relatively split opinion, like the one BioMimetic Therapeutics (Nasdaq: BMTI) received in May. That would be bad news for Affymax, and I've made a CAPScall betting the same. If I'm wrong, there's a lot more room for the stock to move higher, so I'm not sure this is a short candidate, but I'm willing to put my CAPS score on the line.

With too much uncertainty, Affymax didn't make out top stocks for 2012 list, but you can see one that did -- and the reasons why -- by getting our free report, "The Motley Fool's Top Stock for 2012."

Fool contributor Brian Orelli holds no position in any company mentioned. Check out his holdings and a short bio. The Motley Fool owns shares of Johnson & Johnson. Motley Fool newsletter services have recommended buying shares of and creating a diagonal call position in Johnson & Johnson. Try any of our Foolish newsletter services free for 30 days. We Fools don't 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.