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Cabozantinib fails to significantly prolong survival in men with metastatic Castration-Resistant Prostate Cancer
Cabozantinib (XL184) is an oral tyrosine kinase inhibitor with activity against MET and vascular endothelial growth factor receptor 2. Although other VEGFR-targeting agents have failed in prostate cancer, expectations amongst oncologists were high that cabozantinib that also targets c-Met, critical in bone metastasis, would be a winning horse in metastatic castrate-resistant prostate cancer. Preliminary data presented at meetings stirred the oncological community because of reported unprecedented bone scan improvement with complete or partial bone scan resolution (often accompanied by pain relief).
Cabozantinib drug was being evaluated in a Phase 3 clinical trial COMET-1, a randomized, double-blind trial of cabozantinib in 960 men with metastatic castration-resistant prostate cancer (mCRPC) whose disease progressed after treatment with docetaxel as well as abiraterone and/or enzalutamide. All patients in the trial had bone metastases, and there was no limit to the number or type of prior treatments. Patients were randomized 2:1 to receive cabozantinib (60 mg daily) or prednisone (5 mg twice daily).
In a Press Release of Monday, September 1, Exelixis reported on the disappointing results of cabozantinib in advanced prostate cancer men. The South San Francisco biotechnology company announced top-line results from the final analysis of COMET-1. The median overall survival (OS) for the cabozantinib arm of the trial was reported as 11.0 months versus 9.8 months for the prednisone arm, but that difference in overall survival failed to achieve statistical significance (hazard ratio 0.90; 95% confidence interval 0.76 – 1.06; p value 0.212). The trial thus did not meet its primary endpoint of demonstrating a statistically significant increase in overall survival (OS) for patients treated with cabozantinib as compared to prednisone. The company will halt other prostate cancer studies as a result of the outcome of COMET-1 and initiate a significant workforce reduction.