Shares in Dendreon Corp have gone through the roof after the US firm presented highly positive late-stage data on its investigational prostate cancer vaccine Provenge.

The company says that its Phase III IMPACT study of Provenge (sipuleucel-T) in men with advanced prostate cancer met its primary endpoint of improving overall survival compared to placebo. Dendreon highlighted “the magnitude of the survival difference” from the 512-patient study but detailed results will not be presented until the American Urological Association's meeting in Chicago on April 28.

Chief executive Mitchell Gold noted that "survival is the gold standard outcome for oncology clinical trials” and the successful outcome from the IMPACT study “provides validation of the long-pursued goal of harnessing the human immune system against a patient's own cancer".

Some analysts believe that the therapy is destined to be a blockbuster but others are not convinced and most are holding their fire until all the data is revealed as the history of Provenge is leading them towards caution. The US Food and Drug Administration asked for more information the immunotherapy in May 2007 despite one of its advisory committees voting 17-0 in favour of the safety of the drug and 13 to 4 for its efficacy.

That decision, which was based on data that featured a study which only showed a trend toward improvement in overall survival, led to howls of protests from prostate cancer patients. Indeed the FDA was sued over its rejection of Provenge by a group called Care to Live but the lawsuit was dismissed because the agency has still not made a final decision that could be challenged.

Otis Brawley, the American Cancer Society’s chief medical officer, said that the announcement “is reason for optimism about a vaccine that has generated controversy for several years”. He added that “we have to respect the scientific process, an important part of which is a full disclosure and careful review and discussion of the data”. He went on to say that "one of the most important questions we'll be looking at will be the magnitude of the survival advantage” and “we look forward to the presentation of the study at the upcoming meeting."

Dendreon is hoping that the IMPACT study will meet the requirements of the FDA and says that because the data “meet the criteria and specifications outlined in its Special Protocol Assessment agreement” with the agency, it intends to file an amendment to its Biologic License Application in the fourth quarter.

Investors certainly seem to have been convinced and Dendreon shares closed at $16.99, a leap of 132.1%.