Development-stage drugmaker Dendreon (Nasdaq: DNDN) yesterday released "new data" on lead cancer drug Provenge. Unfortunately, the data wasn't the key interim phase 3 survival data that investors are waiting for.

The results were just a different slicing of the data from two relatively small phase 3 studies that are several years old. Dendreon combined the data from these two Provenge studies to see if a patient characteristic or variable was correlated with some important efficacy measure, like survival. 

The drugmaker essentially showed that prostate cancer patients who experienced a particular cellular change after getting Provenge survived longer than patients who didn't experience this particular cellular change. The conclusion that investors are supposed to draw is that Provenge works for some patients. Voila, simple as that.

I know I'm going to sound like a perma Dendreon hater (I'm not), but is a retrospective data analysis rehashed from old studies really that interesting? Dendreon has been slicing and splicing its two phase 3 study results and presenting them at conferences for years now. Even more, Dendreon has already publicly presented the data that it announced yesterday, so it can hardly be considered "new data."

Sure, some of the retrospective data that Dendreon presents may prove to be clinically useful ... if Provenge makes it to market, but there's still the little detail of Provenge needing to prove its overall survival efficacy in the ongoing IMPACT phase 3 trial. The first interim survival data from IMPACT will arrive around the middle of this year, and unless the overall survival results come out positive, nothing else matters.

It's easy to get excited whenever a drugmaker like Dendreon or Genentech (NYSE: DNA) presents "new data" that shows its lead drug may improve cancer patient survival, as Dendreon trumpeted in a press release yesterday or Genentech did earlier in the week for Avastin.

Still, the devil is always in the details with an oncology drugmaker's survival data, which is something I overlooked last year with GPC Biotech (Nasdaq: GPCB), for example. For your sake, be smart and take a close look at whether a drugmaker's survival data is clinically meaningful and, more importantly, will the data help its drug get regulatory approval. In Dendreon's case, the data presented yesterday ends up meaning nothing on the second point; Provenge's approval is tied solely to positive IMPACT data.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool has an A+ disclosure policy.