Updated from 9:18 a.m. EDT

Shares of Dendreon ( DNDN) soared Tuesday after the company said its prostate cancer vaccine Provenge significantly prolonged the overall survival of patients compared to a placebo.

The Seattle-based drugmaker said the phase III study of Provenge, known as IMPACT, met its primary endpoint with statistical significance. Details of the study are being withheld so that they can be presented at a medical conference April 28.

Dendreon shares were rising 175% to $20.10 in recent trading.

"Survival is the gold standard outcome for oncology clinical trials, and overall survival was the primary endpoint of the IMPACT trial. The positive results from this landmark study provide confirmatory evidence demonstrating that treatment with PROVENGE may prolong survival," said Dendreon CEO Mitch Gold, in a statement.

The company plans to submit the new Provenge data to the U.S. Food and Drug Administration in the fourth quarter. Assuming a six-month review, an approval decision could come in the second quarter of next year.

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.

On a conference call Tuesday morning, Gold said that the Provenge results from the IMPACT study were "unambiguous" and "consistent" with previous studies of the cancer vaccine.

The IMPACT study was designed to reduce the risk of death in prostate cancer patients by 22%. Previous studies of Provenge showed the drug to prolong survival by 4.5 months over placebo.

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