When a biotech says that its clinical trial failed its primary endpoint, but appears to be working in a subset of patients, you should stop reading the press release and run away. That is unless the drug treats a disease with relatively few treatment options, and looking at the subset makes biological sense. In that event, you should read further. (But lace up those shoes, just in case.)

The latter applies to Vertex Pharmaceuticals , which announced yesterday the results of its trial testing its cystic fibrosis drug Kalydeco. In patients with a mutation called R117H, the 117th amino acid is changed from an arginine to a histidine, in case you were wondering.


Technically, the trial failed. There was a 2.1 percentage point difference in percent predicted FEV1 -- the amount of air that can be exhaled in one second -- between patients taking Kalydeco, and those taking placebo. The difference wasn't statistically significant.

But when Vertex looked at just the adults in the trial, which it was planning on doing before the trial started, the difference was a solid 5.0 percentage points, which was statistically significant. It turns out, the young kids in the analysis of the full trial data are skewing the data. For kids 6 to 11, those taking placebo actually improved, while those on drug declined slightly.

Will the Food and Drug Administration buy it?
Vertex plans to share the data with the FDA to see if the agency thinks the subset data is compelling enough to put on the label, which would allow Vertex to market the drug for R117H patients.

If this was your run-of-the-mill disease with multiple treatment options, there's no doubt the FDA would tell the company to run another trial; by statistical norms, all secondary endpoints are meaningless if a trial failed its primary endpoint.

Of course it makes sense that adults in decline would be more likely to respond to a drug than kids who are still close to normal; clearly, there's some variation in the FEV1 readouts in young children if the placebo group improved.

Besides Kalydeco, there aren't any drugs available for treating the underlying disease in cystic fibrosis patients. Current treatments, such as Gilead Sciences' Cayston and Novartis' Tobi, are antibiotics that help fight infections caused by mucus buildup in the lungs. Kalydeco attempts to fix the problem that causes the mucus buildup in the first place.

Does an expanded approval really matter?
Worst case scenario, the FDA asks Vertex to run a clinical trial in adults only with R117H patients, putting a potential approval in that indication years away.

But in the meantime, the data is still out there for doctors to see. Vertex can't market Kalydeco for that indication, but the biotech can present the data at scientific meeting, and publish it in a peer-reviewed journal. If doctors are convinced the drug can help their patients, they can prescribe it off label, because Kalydeco is already on the market to treat another mutation.

Insurers could push back and refuse to pay for the drug in R117H patients, but if it improves lung function and helps patients use less of Gilead Sciences' and Novartis' antibiotics, the financial impact might not be enough to justify the backlash that comes with refusing to pay for a doctor-recommended treatment.

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The article Not-So-Solid Data Might Be Good Enough for Vertex originally appeared on Fool.com.

Fool contributor Brian Orelli has no position in any stocks mentioned. The Motley Fool recommends Gilead Sciences and Vertex Pharmaceuticals. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.

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