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What: Shares of Rigel Pharmaceuticals (NASDAQ:RIGL) imploded today, losing as much as 37% of its value after licensing partner AstraZeneca (NYSE:AZN) announced that the first phase 3 study of Fostamatinib failed to meet one of the two designed primary endpoints of the trial.
So what: Fostamatinib -- a treatment for rheumatoid arthritis, or RA, which is a progressive disease that causes inflammation of the joints and surrounding tissues – achieved a statistically significant improvement in the ACR20 response rate in terms of symptoms for both dosage subsets at 24 weeks. However, it didn't show any improvement with regard to progression of joint damage according to x-ray tests. Further, Fostamatinib was generally well-tolerated in trials, but it once again did lead to hypertension, which is a concern not taken lightly by the Food and Drug Administration.
Now what: That's now two strikes for Rigel Pharmaceuticals with Fostamatinib -- one more and it and the drug can take a seat on the bench as far as I'm concerned. In December, Fostamatinib proved to be an inferior treatment option for patients with RA in a direct comparison to AbbVie's (NYSE:ABBV) blockbuster drug Humira -- strike one. Today, it failed to demonstrate any statistically significant improvement in suppressing joint damage -- strike two. Tack on the fact that Pfizer's (NYSE:PFE) Xeljanz, another FDA-approved treatment for RA, scored higher than Fostamatinib in its ACR20 response rate in its phase 3 tests and doesn't have hypertension concerns, and you can see that even if Fostamatinib somehow gains approval, its uses appear to be extremely limited. Rigel still has two additional late-stage trials ongoing with Fostamatinib, but the expectation that they will be a success are quickly waning.
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Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.
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