Prostate cancer treatment zibotentan is looking like less of a threat to Dendreon's (Nasdaq: DNDN) Provenge after AstraZeneca (NYSE: AZN) said that it was stopping a phase 3 trial testing zibotentan in prostate cancer patients.

An interim look at the data suggested zibotentan wouldn't extend survival in non-metastatic prostate patients. AstraZeneca decided to take the preliminary peek after a clinical trial failed to show that zibotentan helped patients with metastatic prostate cancer last year.

Zibotentan has failed in both early- and late-stage prostate cancer, but Dendreon isn't completely out of the woods yet. Both of those trials were testing zibotentan as a monotherapy, and AstraZeneca still has one more trial testing zibotentan in combination with sanofi-aventis' (NYSE: SNY) Taxotere.

That trial, which will read out in the second half of the year, is the biggest threat to Provenge; if a zibotentan-Taxotere combination works better than Taxotere alone, it could end up extending survival longer than Provenge. Given the data to date, that seems like a long shot, but if zibotentan has any activity, combining it with the survival benefit from Taxotere would seem to be the easiest way to see an effect.

Provenge could also see competition from Sanofi's Jevtana and Johnson & Johnson's (NYSE: JNJ) abiraterone, although probably not for a while. Both drugs appear to help patients that have failed Taxotere, but until they're tested in patients earlier in their disease progression -- the time when Provenge is used -- they won't be a threat to Provenge.

For now, my pick for the best stock of 2011 seems free from immediate competition other than wimpy Taxotere. As long as Dendreon can get its manufacturing ducks in a row, sales should continue to roll in.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.