UPDATED: Onyx clears big hurdle in high-stakes gamble on early carfilzomib approval

Onyx's ($ONXX) risky attempt to win an approval for the multiple myeloma drug carfilzomib on the basis of mid-stage data from a single-arm study cleared a major hurdle yesterday evening when an FDA advisory group gave its drug a unanimous thumbs up.

By a vote of 11 to 0--with one abstention--the panel concluded that a host of severe risks, the death of 5 patients and a questionable benefit did not outweigh the therapy's potential to help a group of cancer victims who had run out of options. And they appeared content to push for an approval now on mid-stage data for the proteasome inhibitor rather than force the company to wait and see if an ongoing late-stage study confirmed what investigators found in Phase II.

"This is an unmet need in a group that has really run out of options," noted panel chair Wyndham Wilson, according to a Bloomberg report. "There is a pretty convincing signal here that is likely, I believe, to be confirmed in confirmatory trials."

The outcome was something of a shocker for some analysts who had predicted that the experts would give carfilzomib's investigators something of a trial by fire yesterday. And investors responded eagerly, bidding up the biotech's shares by 37% on the outcome.

Onyx isn't out of the woods yet, though. FDA staffers turned a bright light on their concerns with the "severe toxicities" associated with carfilzomib, questioning whether a study in which the drug shrunk tumors in 22% of patients warranted patients' exposure to the treatment. And the FDA has traditionally looked askance at single-arm studies, which leave open the relative benefit of a treatment compared to the standard of care. 

But, if Onyx does win this approval, the company gets a big boost at a time it's widely rumored to be on the auction block, with longtime partner Bayer in particular cited as a likely bidder. A number of analysts have estimated potential sales above the $500-million-a-year mark. An approval would also encourage more drug developers to make their case for cancer drugs on Phase II data, significantly changing the value of these products if regulators appear more willing to take these risks among the sickest patients. And that process could be further accelerated by the new PDUFA bill that's about to clear Congress.

Onyx acquired carfilzomib in its buyout of Proteolix back in 2009 for $276 million in cash and $535 million in milestones. The PDUFA date for the formal decision is July 27.

- here's the report from Bloomberg
- read the Wall Street Journal story