Exelixis said last night it will eliminate about 70% of its workforce,160 jobs, following the Phase III failure of its metastatic castration-resistant prostate cancer (mCRPC) treatment cabozantinib in a study comparing the experimental drug to prednisone.

“We have thoughtfully prepared for this scenario and the resulting very difficult decisions. The workforce reduction we have announced today is necessary to significantly reduce our corporate operating expenses,” Michael M. Morrissey, Ph.D., Exelixis’ president and CEO, said in a statement. “We are very disappointed that COMET-1 did not meet its primary endpoint of extending overall survival in men with mCRPC.”

Exelixis said cabozantinib, a tyrosine kinase inhibitor, did not meet its primary endpoint of demonstrating a statistically significant increase in overall survival (OS) for patients compared to prednisone in the COMET-1 trial, according to top-line results.

The Phase III study assessed the effectiveness of cabozantinib and prednisone in 960 patients with mCRPC whose disease progressed after treatment with docetaxel as well as abiraterone and/or enzalutamide. Patients were randomized 2:1 to receive cabozantinib (60 mg daily) or prednisone (5 mg twice daily).

COMET-1 yielded a median OS for patients treated with cabozantinib of 11 months, compared with 9.8 months for the prednisone arm. Median progression-free survival (PFS) was 5.5 months for the cabozantinib arm versus 2.8 months for the prednisone arm. Safety data were consistent with those observed in earlier-stage trials of cabozantinib in mCRPC.

Back in March, Exelixis wrapped up an interim analysis of COMET-1 data by saying it would see the trial through to its conclusion. That announcement touched off a sell-off of shares by investors who compared cabozantinib unfavorably to three other CRPC treatments introduced to market following the release of positive interim data—Zytiga® (abiraterone acetate; Johnson & Johnson’s Janssen Biotech), Xtandi® (enzalutamide; Astellas Pharma and Medivation), and Xofigo® (radium Ra 223 dichloride; Bayer HealthCare).

Exelixis said COMET-1 results “are the subject of ongoing analyses” and that the company will submit additional data, including secondary and exploratory endpoints, for presentation “at a future medical conference.”

However, Exelixis said it “deprioritized” the clinical development of cabozantinib in mCRPC based on the outcome of COMET-1, and has halted enrollment in other company-sponsored studies in mCRPC. Those studies include a randomized Phase II study of cabozantinib in combination with abiraterone; and COMET-2, a second Phase III study of cabozantinib in mCPRC patients that was designed to evaluate pain palliation in patients.

The company said it expects top-line data on COMET-2 before year’s end. Based on that data, Exelixis said, it will discuss with authorities the potential regulatory path of cabozantinib in mCRPC.

Exelixis said it will take a one-time charge of between $6 million and $8 million toward the layoffs, which will shrink the company’s workforce to 70 employees. Exelixis said it will focus its spending going forward on late-stage clinical trials in progress for cabozantinib in two other oncology indications, metastatic renal cell carcinoma (the METEOR trial) and advanced hepatocellular carcinoma (the CELESTIAL trial).

The company expects top-line results from METEOR in 2015, and from CELESTIAL two years later, Morrissey said.

Exelixis has sought to expand the approved indications for cabozantinib, which has been marketed for the treatment of progressive, metastatic medullary thyroid cancer (MTC) since its approval by the FDA in 2012. In Europe, the drug is approved conditionally for adult patients with progressive, unresectable locally advanced or metastatic MTC.

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