Cabozantinib active in castration-resistant prostate cancer

David C. Smith, M.D., of the University of Michigan in Ann Arbor, and colleagues conducted a phase II randomized discontinuation trial involving 171 men with CRPC to evaluate the activity of cabozantinib. Patients received 100 mg of cabozantinib each day, and those with stable disease at 12-weeks were randomized to receive cabozantinib or placebo.

Based on the observed activity of cabozantinib, random assignment was stopped early. The researchers found that 72 percent of patients had regression in soft tissue lesions and 68 percent exhibited improvement on bone scan, including 12 percent with complete resolution. At 12 weeks, the objective response rate was 5 percent, and 75 percent exhibited stable disease. The median progression-free survival was 23.9 and 5.9 weeks for cabozantinib- and placebo-treated patients, respectively (hazard ratio, 0.12). In 57 percent of patients, there was a reduction of at least 50 percent in serum total alkaline phosphatase and plasma cross-linked C-terminal telopeptide of type I collagen. In a retrospective data review, bone pain was improved for 67 percent of patients, and narcotic use decreased by 56 percent. Fatigue, hypertension, and hand-foot syndrome were the most common grade 3 adverse events.

"Cabozantinib has substantial antitumor activity in patients with advanced CRPC with manageable toxicity consistent with other tyrosine kinase inhibitors targeting multiple pathways," the authors write.

Several authors disclosed financial ties to pharmaceutical companies, including Exelixis, which manufactures cabozantinib and supported the study.

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Journal reference: Journal of Clinical Oncology

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