What happened

Exelixis (NASDAQ:EXEL) ended the day up 12% after announcing that the blinded independent radiology review committee confirmed the progression-free survival as measured by the investigators of the CABOSUN clinical trial.

So what

CABOSUN was a phase 2 trial testing Exelixis' Cabometyx against Pfizer's (NYSE:PFE) Sutent in patients with previously untreated advanced kidney cancer with intermediate- or poor-risk disease. The clinical trial wasn't really designed to gain approval for Cabometyx -- it was a phase 2, trial after all -- but the results were outstanding, with Cabometyx showing a clear benefit over Sutent, the current standard of care treatment for first-line kidney cancer. Cabometyx is currently approved as a second-line treatment after patients fail Pfizer's drug.

Rather than go with the investigator-assessed progression-free survival, which can be tainted by doctors' opinions since they can often tell which drug a patient is on by the side effects, Exelixis decided to get all the patients' scans reviewed again by a group of independent reviewers who were blinded to which drug the patients were taking, to determine when the patients' tumors started growing again.

As noted, the independent reviewers came to the same conclusion: Cabometyx extends progression-free survival longer than Sutent.

A doctor talks to a patient in a hospital bed.

Image source: Getty Images.

Now what

With this adjudicated data in hand, Exelixis is on track to file its supplementary new drug application with the Food and Drug Administration in the third quarter. It's not a perfect application, since CABOSUN wasn't designed to gain approval, but given the solid results, it seems likely that the FDA will sign off on the expanded application.

It's debatable whether Exelixis deserved a double-digit gain for proving that the CABOSUN data is real, but considering shares had pulled back off their 52-week high, it seems that at least some investors were worried the investigator-assessed data was tainted.