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to patients with less-aggressive tumor types, as ranked by Gleason scores, because at the time, Dendreon thought Provenge had a better chance of working for those patients. When later data suggested the benefit was more widespread across patient populations, it asked the FDA to amend the study to allow all comers into the trial, including those with tumor types that had spread and who had relapsed after prior hormone-deprivation therapies.
Dendreon, of course, tried and failed to win FDA approval in 2007 based on the earlier set of data, which is a long story that I wrote about on April 3. But once it became clear it needed to produce good results from Impact to get approval, Dendreon had an idea for how to speed up results.
Because Dendreon was eager to turn it its application to the FDA, it negotiated for the right to take an early peek at the data from the Impact study in the fall of 2008, a practice known as an interim analysis. This meant that if the drug was obviously showing a survival benefit as data started trickling in, Dendreon could whip up a faster application to the FDA and bring it to the market sooner. It also meant that it would introduce some bias into the study, and that FDA statisticians would insist on Dendreon clearing a higher statistical bar than usual when the final analysis comes in. The FDA standard for statistical significance is when a trial has a p-value of 0.05 or less, with the smaller number being the better number. Dendreon has not disclosed how much of a p-value penalty it paid for taking that early peek, but it’s safe to say it will need to show a p-value of something a fair bit lower than 0.05 to win over its skeptics.
The Impact trial was designed to primarily measure survival time in men whose prostate cancer had spread and resisted prior therapies. It was meant to succeed if it were consistent with the earlier results, showing a 22 percent reduced chance of death during the study, known in biostats parlance as a hazard ratio. The side effects from earlier studies were mild fever and chills that typically lasted a couple of days after Provenge injections. This is the advantage many patients are excited about, because hormone deprivation amounts to chemical castration, and chemotherapy is also known for its rough side effects.
Dendreon didn’t compare Provenge head-to-head in this clinical trial against the standard of care for this terminal form of prostate cancer, docetaxel (Taxotere) from Sanofi-Aventis. This competing drug produced a median survival of 19.3 months in its pivotal clinical trial, called TAX-327, which was about a 3-month advantage compared with a placebo. About one-third of patients suffered serious side effects.
Although it’s always dangerous to compare one clinical trial to the next, people always do anyway, and Provenge’s Impact data is likely to stack up well side-by-side, says David Miller, CEO of Seattle-based Biotech Stock Research. He has developed a “cheat sheet” to compare the most important data points from the trials side by side.
The Impact study is likely to show it is somewhat better than Taxotere, although probably something short of the results seen in the earlier Provenge trial called 9901, Miller said in a note to clients on April 26. “As long as that is true, we expect little long-term drama even though the price will vary wildly depending on where the Impact data falls in this bracket,” Miller wrote.
Dendreon continued to surge in trading yesterday, climbing $1.47 to close at $21.55 at the close on more than triple the average trading volume. Today could be an even bumpier ride depending on what the company says to an audience of physicians at the McCormick Place convention center in Chicago.
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