Phase II study of XL 184 (Exelixis) shows significant improvement in patients with castration-resistant Prostate Cancer

About two-thirds of patients with castration-resistant Prostate Cancer treated with XL 184 (cabozantinib), from Exelixis, had improvements on their bone scans, with 12 percent seeing complete resolution of uptake on bone scan, according to results of a Phase II study. The trial enrolled 171 men with castration-resistant Prostate Cancer, and began as a randomized trial in which all patients received cabozantinib for 12 weeks, after which patients were randomized to receive continued cabozantinib or placebo. The randomization was stopped early because of the dramatic effects on bone scan, and because patients receiving placebo saw their cancer progress much more quickly than those that remained on drug.

Among the 31 patients who were randomized, cancer progressed after a median 23.9 weeks for patients taking cabozantinib, compared with 5.9 weeks for patients on placebo. In addition to the improvements on bone scans, 67 percent of patients with bone pain reported an improvement in pain control and 56 percent decreased or eliminated narcotic painkillers after treatment with cabozantinib. Results of the study appear in the Journal of Clinical Oncology. See: "Cabozantinib in Patients With Advanced Prostate Cancer: Results of a Phase II Randomized Discontinuation Trial" David C. Smith et al. Journal of Clinical Oncology, online November 19, 2012; DOI:10.1200/JCO.2012.45.0494