Investors didn't seem to know what to make of Dendreon's (NASDAQ:DNDN) announcement of interim data from its phase 3 trial -- called IMPACT -- for its Provenge prostate-cancer treatment yesterday. The company's stock managed to hit a 52-week high and almost reached a 52-week low. Now that's some serious volatility.

In the end, though, investors seem more excited than not about the results, with the stock settling up 33%. But was the data really that good?

Well, the results weren't good enough to get the drug approved by themselves. Dendreon will have to wait until the final results are available in the middle of next year before it can apply for Food and Drug Administration approval -- again. But not many people were expecting Dendreon to be able to clear the high hurdle it set for itself, so the results weren't a total setback.

Perhaps the best thing that can be said about the results was that they weren't horrible. If they had been bad enough -- a safety issue, for instance -- the independent data-monitoring committee could have stopped the trial; the committee monitoring Onyx Pharmaceuticals' (NASDAQ:ONXX) Nexavar lung-cancer trial did just that, though for a different reason than safety. Given that patients taking Cell Genesys' (NASDAQ:CEGE) prostate-cancer treatment GVAX, in combination with Taxotere from Sanofi-Aventis (NYSE:SNY), died at a much higher rate than patients in the group taking just Taxotere, I could see how investors might breathe a sigh of relief after hearing that the trial hadn't been stopped.

Provenge did show a trend toward increased survival, reducing the risk of death by 20% compared to placebo. In order to gain final approval next year, that number will have to be above 22%, the study's endpoint goal. While that may not sound like all that much, remember that all the patients in the interim result will be counted in the final results. Therefore, the patients getting Provenge still left to be counted will have to survive at significantly greater rates than those receiving placebo in order to raise the survival risk above the threshold.

The good news is that there's some evidence that Provenge is late-acting. In previous trials, Provenge reduced the risk of death further as the trials went on.

So should you jump on the Dendreon roller coaster? Only if you really like volatility. Still, with no major events to move the stock for the next nine months or so, there's plenty of time to hop on board. In the meantime, check out some drug developers with multiple shots on goal, like Seattle Genetics (NASDAQ:SGEN) or Exelixis (NASDAQ:EXEL).

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool owns shares of Exelixis. The Fool's disclosure policy reduces your risk.