Prostate cancers initially need the male hormone testosterone for growth. Hormone therapies that lower the level of testosterone are among the most effective treatments for prostate cancers that have spread to other organs (metastasized). The benefits of hormone treatments do not last, however. Over time, many prostate cancers continue to grow despite hormonal therapies (and are called “castration-resistant” prostate cancer).
In this study, researchers want to compare the effectiveness of the investigational drug cabozantinib (XL184) with standard therapy (prednisone) in men with metastatic castration-resistant prostate cancer that continued to spread despite prior treatment with docetaxel and either abiraterone or MDV3100 (enzalutamide). Cabozantinib blocks several proteins (called MET, RET, and vascular endothelial growth factor receptor 2) that help keep cancer cells alive. It is a capsule that is taken orally (by mouth).
Patients will be randomly assigned to receive cabozantinib (2/3 of the patients) or prednisone (1/3 of the patients), but not both. Patients in each group will also receive a placebo pill that is similar to the drug that the other group is taking. Researchers will evaluate the effects of these treatments on bone metastases and survival.