CHICAGO -- The U.S. Food and Drug Administration has all the data it needs now to finally approve Dendreon's ( DNDN) prostate cancer vaccine Provenge, says the researcher who presented the Provenge study results Tuesday.

"These data answer all the questions raised two years ago by the FDA. I think they will approve it," said Dr. David Penson, a professor of urology at the University of Southern California and an investigator in the Provenge study.

The FDA refused to approve Provenge two years ago despite data from previous clinical trials showing the drug extended survival by 4.3 months in men with advanced prostate cancer. At that time, regulators asked Dendreon to provide more proof that Provenge could prolong survival.

That proof came Tuesday at the annual meeting of the American Urological Association.

Penson presented the final data from Dendreon's phase III IMPACT study showing that Provenge prolonged survival by 4.1 months in men with advanced prostate cancer. After three years, 31.7% of Provenge-treated patients were alive, compared to 23% for control patients -- a 38% improvement. The results were statistically significant.

The 4.1-month survival benefit was on the upper end of expectations and exceeds the survival advantage provided by Taxotere, a chemotherapy drug marketed by Sanofi Aventis ( SNY).

To put these results in perspective, very few cancer drugs can make the claim of a survival benefit greater than four months. Only one drug has had that kind of impact recently -- Genentech's Avastin, which improved survival in advanced colon cancer patients by 4.7 months.

"I'm already getting calls weekly from patients wondering when Provenge will be approved," said Penson.

Dendreon CEO Mitch Gold said the company would re-file Provenge with the FDA in the fourth quarter.

"The results of the Provenge study are unambiguous," said Gold on a company conference called Tuesday night, adding that if the FDA takes six months to review Provenge again, the drug could be on the market in the middle of 2010.

The IMPACT study enrolled 512 men with advanced prostate cancer who no longer responded to hormone therapy. The primary endpoint of the study was to determine whether treatment with Provenge prolonged overall survival of patients compared to a placebo.

Dr. Robert Reiter, a professor of urology at the UCLA Jonsson Comprehensive Cancer Center and a self-described Provenge skeptic was in the audience to see the Provenge presentation, and walked away impressed.

"Four months of survival including crossover probably means that the survival benefit may be even higher, with no significant toxicity. While I would have liked to see some data showing Provenge improving quality of life, if the drug is approved and paid for, there are not going to be a lot of reasons not to use it," he said.

By crossover, Reiter is referring to a rule in the study that allowed patients in the control arm to receive a frozen form of Provenge once their prostate cancer progressed. This set a higher bar for Provegne to show a survival benefit.

While Provenge's survival benefit was robust, the drug did not shrink tumors or stop them from growing. The study was also not designed to measure whether patients enjoyed an improved quality of life.

Penson, however, says the drug's clean safety profile and ease of administration makes patients feel better.

"I don't have hard quality-of-life data, but in my gut after treating patients, I do believe that Provenge improves quality of life," he says. "A patient can get this drug on a Friday and play golf on Saturday. That's not an exaggeration; that's a fact."

Adam Feuerstein writes regularly for TheStreet.com. In keeping with TSC's editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet.com. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.