Exelixis' cabozantinib misses main goal of second Phase III prostate cancer study

Exelixis announced Monday that the experimental therapy cabozantinib failed to meet the primary endpoint of a Phase III trial of alleviating bone pain compared to mitoxantrone/prednisone in men with metastatic castration-resistant prostate cancer (mCRPC) who experienced moderate to severe pain despite optimised narcotic medication. Shares in the drugmaker fell as much as 10 percent on the news.

In the COMET-2 study, 119 men, of a total planned enrolment of 246 patients, with mCRPC who experienced moderate to severe pain despite optimised narcotic medication and whose disease progressed following treatment with docetaxel as well as Johnson & Johnson's Zytiga (abiraterone) and/or Astellas and Medivation's Xtandi (enzalutamide) were randomised to receive cabozantinib or mitoxantrone/prednisone. The main goal of the study was a pain response, defined as an at least 30 percent decrease from baseline in the mean daily worst pain intensity according to the BPI collected over seven days at week six that was confirmed at week 12 without an increase in narcotic therapy.

Study results demonstrated that 15 percent of men in the cabozantinib arm reported a pain response, compared to 17 percent of men in the mitoxantrone/prednisone arm. Secondary endpoints of the study included progression-free survival, safety, and the evaluation of bone biomarkers and circulating tumour cells.

In September, Exelixis reported that cabozantinib failed to improve overall survival versus prednisone in the COMET-1 trial. CEO Michael Morrissey remarked "we deprioritised the cabozantinib development programme in mCRPC [in September]; at that time, we also initiated a significant workforce reduction in order to focus our development efforts and financial resources on the pivotal phase III studies of cabozantinib in metastatic renal cell carcinoma (RCC) and advanced hepatocellular carcinoma." Morrissey noted that top-line results in the METEOR trial of cabozantinib in the treatment of RCC are expected in the second quarter of next year.

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