In an interesting tactical move, Dendreon (NASDAQ:DNDN) announced yesterday that it had reached an agreement with the FDA to amend its pivotal phase 3 study for its prostate cancer treatment Provenge.

Dendreon has been testing its lead drug in a large 500-person phase 3 clinical trial dubbed IMPACT; it received an FDA approval letter for the compound last year. IMPACT is Dendreon's last near-term chance to get Provenge onto the market. To gain approval, the drug needs to show an overall survival advantage in this study versus the control group.

The study gives Dendreon two chances to show a survival advantage with Provenge. The first is expected to come in the second half of this year, when Dendreon takes an interim peek at the overall survival data. If that look shows no discernable advantage, Dendreon will still have until the end of the study in 2010 to show a survival benefit.

The downside to taking an interim look at a study's data is that the hurdle at the interim for showing positive efficacy is higher than at the end of the study. Dendreon has never revealed this interim overall survival data hurdle, but if the FDA has treated Provenge like it has other cancer drugs, such as GPC Biotech's (NASDAQ:GPCB) cancer compound last year, it's likely high.

Dendreon essentially announced yesterday that the FDA agreed to allow it to move the study's expected final data reveal into the second half of 2009, rather than 2010, in exchange for making the interim 2008 data peak hurdle even higher. While few details were revealed, this toughening up of the interim data hurdle probably nixes any possibility that Provenge might get onto the market before 2010, barring extremely positive survival data later this year.

Dendreon hasn't yet provided any information on why it chose to trader lower interim positive data odds for faster final data. The drugmaker will hold a conference call today to discuss this strategic move.

I can't say I'm a fan of this move. I'd much rather Dendreon take a more conservative approach, keeping the study's final data point in 2010 to maximize any chance that Provenge does show positive data. This same sort of corner-cutting and playing with efficacy endpoints may have gotten Dendreon in trouble with its first two phase 3 studies.