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What: Shares of Exelixis (Nasdaq: EXEL) are soaring by as much 26% today after the company announced positive preliminary results from a phase 3 clinical trial for cabozantinib.

So what: The drug is intended for patients with advanced medullary thyroid cancer, and the trial met its primary endpoint of improving progression-free survival compared with placebo. It substantially exceeded the threshold of a 75% increase in PFS assumed at the onset of the trial.

Now what: Cabozantinib significantly improved median PFS by 7.2 months relative to the placebo. Exelixis CEO Michael Morrissey called the results "an important advance for MTC patients and for Exelixis." The company will consult with the Food and Drug Administration and is hoping to begin a rolling submission of a new drug application. Exelixis hopes that the filing will be completed by the first half of 2012.

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