How many patients need to be "cured" of a disease to send a stock up more than 22%? Apparently just two.

That's right, two. A couple, a pair, dos, deux. However you say it, it's a mighty small number.

The euphoria, which waned a little as Medarex (NASDAQ:MEDX) ended up just 12.5%, came from a Mayo Clinic report that two prostate cancer patients in a clinical trial testing the company's cancer drug ipilimumab had become cancer-free.

The report wasn't the full results of a clinical trial. It wasn't published in a peer-reviewed journal. It was published in Discovery Edge, which, as far as I can tell, is a self-published magazine for the hospital to promote itself to potential donors. There's nothing wrong with that -- I get a glossy look-how-great-we-are magazine from my alma mater too -- but let's not confuse incidental reports with a full-fledged clinical trial.

According to ClinicalTrials.gov, the phase 2 clinical trial is still recruiting patients -- although one has to think this news will fill it up fast -- and the full results from 54 treated patients aren't expected until June of next year.

That being said, there is reason to be cautiously optimistic. Helping a patient with advanced prostate cancer become free from the disease is pretty darn impressive; sanofi-aventis' (NYSE:SNY) Taxotere and Dendreon's (NASDAQ:DNDN) Provenge extend survival by a few months on average. Some patients on Provenge have reportedly lived for years, but I don’t know of any reports that they've become cancer-free.

Medarex has royalty-bearing licenses for its antibody technology with a few companies, including Johnson & Johnson (NYSE:JNJ) and Novartis (NYSE:NVS), but ipilimumab, which it'll market with Bristol-Myers Squibb (NYSE:BMY), is the company's most advanced internally developed drug. Ipilimumab hit a snag last year when the FDA decided that the companies needed to run a longer trial before submitting the data to approve ipilimumab for melanoma.

The reports in prostate cancer patients should give investors a little hope that the melanoma trial will be successful, but keep in mind that each cancer type is different and melanoma is about as difficult to treat as they come.

Be optimistic, Fools, just don't go all in. There's a lot that can go wrong between now and when the drug gets approved.

But feel free to go all in on this Foolishness:

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Johnson & Johnson is a Motley Fool Income Investor recommendation. Novartis is a Global Gains recommendation. The Fool has a disclosure policy.