Well, I was half right. I guessed incorrectly that Affymax (Nasdaq: AFFY) wouldn't get past its Food and Drug Administration advisory panel with anything better than a split decision. Instead, the advisors voted 15-1, recommending that its anemia drug, peginesatide, be approved.

But to my credit, I also cautioned that there wasn't much reason to short the stock, either. "There's plenty of upside if the FDA approves peginesatide, because it isn't clear that it will," I wrote. Betting against the crowd paid off big time for those who held shares through the advisory panel meeting. Affymax is soaring, closing up more than 36% today.

The panel of outside experts basically blew off the data that peginesatide increases cardiovascular risk in patients not on dialysis. After that data came in, Affymax and Takeda changed course and applied for approval only in patients on dialysis, where the cardiovascular risk wasn't seen. The doctors on the panel, with the exception of one, were clearly OK with that.

Affymax is in a much better position than it was before the advisory panel meeting, but the company isn't out of the woods yet. The FDA doesn't have to take the advisory panel's advice and is often more cautious than panel members, something Dendreon's (Nasdaq: DNDN) and InterMune's (Nasdaq: ITMN) investors know all too well.

And investors seem to realize that; there's plenty more upside if an approval happens. Investors are valuing the company at only $300 million. Even assuming a very conservative price-to-sales ratio of 3, there's only $100 million of sales priced in. By comparison, Amgen's (Nasdaq: AMGN) Epogen had sales of $476 million in just the third quarter alone. Johnson & Johnson (NYSE: JNJ) sells the same compound -- epoetin alfa -- as Procrit for treating anemic cancer patients, so there's more potential there, too.

Even though Affymax's drug is superior to Epogen because it has to be infused only once a month, the company might be best off undercutting its competitor to hopefully grab market share quickly. Affymax can look to Regeneron Pharmaceuticals' (Nasdaq: REGN) Eylea, which the company recently priced under Roche's competing macular degeneration drug, to see whether the strategy works.

Expect that shares may remain volatile up through the March 27 PDUFA date. I'll leave the predictions to you. Take our poll, and let us know the reason for your vote in the comments box.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.