Peregrine's Epic Failure (Maybe)


Clinical trial 101 says if a trial passes all of its primary endpoints it's successful. If it doesn't, it's not. With some exceptions -- non-inferiority trials, for instance -- passing is usually defined as a statistically significant difference between the drug arm and the placebo arm.

Unfortunately, investors are left to wonder whether Peregrine Pharmaceuticals' phase 2 trial testing bavituximab in pancreatic cancer was successful. There wasn't one p-value -- the measurement of statistical significance -- cited in the whole press release.

It seems we'll have to assume then that the improvement in overall survival, the primary endpoint, wasn't statistically significant. The net improvement of just 0.4 months is also a pretty big clue that it didn't meet the threshold for being statistically significant, usually a p-value of less than 0.05. Patients that received bavituximab and gemcitabine had a median survival of 5.6 months versus 5.2 months for patients that got gemcitabine alone.

Peregrine was nice enough to provide us the hazard ratio of 0.75, which translates to a 25% improvement in overall survival, but it's a meaningless number if the improvement isn't statistically significant. For reference, Celgene's trial testing Abraxane plus gemcitabine compared with gemcitabine alone in pancreatic cancer had a slightly better hazard ratio of 0.72, and more importantly the p-value was 0.000015, or put another way, there's a 0.0015% chance that the difference in survival -- 8.5 months vs. 6.7 months -- happened by chance alone.

Peregrine also pointed out that adding bavituximab to gemcitabine doubled the response rate from 13% for patients that only took gemcitabine to 28% for the bavituximab plus gemcitabine arm. But again, no p-value was cited. And overall survival is much more important anyway; causing a tumor to respond to treatment isn't particularly useful if it doesn't result in an increase in survival.

Beyond the lack of full disclosure of the data, Kerstin Menander, head of medical oncology at Peregrine, acknowledged the modest effect and added, "Further analysis of the data including subgroups shows some very interesting and potentially promising trends."

That's all well and good, but the best data mining can do is give you a new hypothesis to test. Investors should watch carefully to ensure Peregrine doesn't follow Aeterna Zentaris and Keryx Biopharmaceuticals' lead, taking their cancer drug perifosine into a phase 3 trial in advanced colorectal cancer patients based on a subset of the phase 2 data; it didn't turn out well. If Peregrine has a new hypothesis, the biotech would be wise to run another cheaper phase 2 trial to test it.

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