Exelixis To Push Ahead on Prostate Cancer Trial Without FDA Agreement: Shares Plunge

10/31/11Follow @xconomy

Exelixis has been talking with the FDA for months about reaching an agreement on the design of a pivotal trial for its prostate cancer drug, but now the company has essentially thrown up its hands and decided to push ahead in testing without any formal regulatory deal.

Shares of the company fell more than 30 percent, to $5.36, in after-hours trading following the announcement.

The drop came after Exelixis (NASDAQ: EXEL) said it was unable to reach a “timely agreement” with the FDA on a special protocol assessment, or SPA, for the pivotal trial of cabozantinib as a treatment for prostate cancer. By negotiating upfront on key elements of a clinical trial—things like the main goal of the study and the statistical analysis plan—biotech companies like Exelixis seek to minimize the risk that their study will be rejected later by the FDA as inadequate.

In this case, Exelixis has shown some compelling data from preliminary studies that its drug can relieve prostate cancer-related bone pain, so it has pushed to make that the primary goal of its pivotal study known as the ’306 trial. While pain relief is an important measurement of progress for patients with advanced prostate cancer, the FDA often insists that cancer drugmakers design their trials to demonstrate an improvement in overall survival time.

Now that Exelixis has opted to go ahead with its trial without overall survival as the main goal, investors are wagering there’s a greater chance the drug will get tied up in regulatory delays. Exelixis, for its part, is saying it can’t afford to keep waiting to start the trial. It plans to begin the trial before the end of 2011. The study is designed to enroll 246 patients with prostate cancer that resists hormone-deprivation therapy, whose tumors have spread to the bone, and which resists treatment with narcotic pain medication.

Mike Morrissey

“We have had a valuable dialogue with the FDA on the ’306 trial protocol and gained important insight throughout this process, including on the definition of pain response and that pain may be an appropriate efficacy endpoint in the phase 3 ’306 trial if the treatment effect is pronounced. The FDA also stated that the trial can be conducted without a SPA under the normal regulatory framework,” said Exelixis CEO Mike Morrissey, in a statement.

The company’s statement today included some commentary from Howard Scher, a prostate cancer specialist at Memorial Sloan-Kettering Cancer Center in New York, who defended the Exelixis trial design. “Effectively managing pain is a particular challenge for symptomatic patients in the metastatic setting,” Scher said. “Cabozantinib has the potential to become an important agent.”

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