If Dendreon ( DNDN) is now king of all cancer vaccines, the company's coronation may come Tuesday inside a Chicago convention hall.

That's where a large crowd of urologists (and perhaps an equal number of investors) are gathering to witness the presentation of data from a pivotal clinical trial of Provenge, Dendreon's cancer therapeutic vaccine.

Dendreon shares are up markedly ever since the company announced April 14 that the phase III Provenge study was successful in extending the lives of men with advanced prostate cancer. Missing from Dendreon's triumphant announcement, however, were any details from the study, including the specifics about Provenge's survival benefit.

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Which is why the annual meeting of the American Urological Association at Chicago's McCormick Place convention center is suddenly so important. The Provenge data, culled from the phase III study known as IMPACT, will be presented at 2:20 p.m. Central Daylight Time.

The continued rally in Dendreon's stock price depends on the actual Provenge data matching, or exceeding, expectations set by the company's April 14 announcement.

What exactly are those Provenge expectations? They're hard to pinpoint precisely, but Dendreon CEO Mitch Gold stated that the survival benefit seen in the IMPACT trial was "consistent" with results in the previous Provenge studies. That suggests a survival benefit favoring Provenge in the range of four to four-and-a-half months compared to patients in the control arm.

The IMPACT study was designed to succeed if Provenge could reduce the risk of death by 22%. Stated statistically, that equates to a "hazard ratio" of 0.78. Again, Dendreon hasn't provided any hard numbers yet, but the company did state that Provenge hit its pre-specified level of statistical significance, which implies at least a 22% reduction in the risk of death.

Dr. Howard Adler, a urologist and director of the Prostate Care Program at the State University of New York, Stony Brook, predicts a four-month survival benefit for Provenge but says that anything more than two to three months will be viewed by most doctors as positive and clinically meaningful for prostate cancer patients.

Taxotere, marketed by Sanofi-Aventis ( SNY), is the only other prostate cancer drug used extensively to treat patients with advanced disease, with a known survival benefit of two to three months.

"If Taxotere could be approved by the FDA with a survival benefit of two to three months, then that should also be good enough for Provenge, especially since Provenge is going to be safer and more easily tolerated than Taxotere," said Adler.

While the Provenge data appear to be very positive, not everyone is a believer just yet.

Dr. Robert Reider, a professor of urology at the UCLA Jonsson Comprehensive Cancer Center, is a self-described Provenge skeptic in part because he's uncomfortable that Provenge appears to prolong patient survival without having any measurable effect on the tumor itself.

"In all the studies to date, Provenge has not stopped tumors from shrinking, nor has it had any positive effect on a patient's quality of life or PSA scores," said Reider. PSA is a protein marker found in blood used to detect prostate cancer.

"There has never been a drug approved that improved survival yet had no impact on the disease itself," Reider added, although he conceded that Provenge may well be the first if the drug posts a strong survival benefit Tuesday afternoon.

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.

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