Trial of Cabozantinib (XL184) in Castrate-Resistant Prostate Cancer Metastatic to Bone

Inclusion Criteria: * Pathologically and radiologically confirmed castrate-resistant prostate cancer metastatic to bone * Bone metastases which are accessible for biopsy under CT guidance. * Willingness to undergo sequential biopsy of bone lesions. * No prior standard chemotherapy for metastatic disease (neoadjuvant, adjuvant and hormonal treatments are excluded). * Participant must have discontinued antiandrogen therapy at least 4 weeks (for flutamide and megestrol acetate) or 6 weeks (for bicalutamide or nilutamide) prior to the first dose of XL184. Participants currently on LHRH or GnRH agonists can be maintained on these agents. * Greater than or equal to 18 years old on day of consent * Participants must be able to care for themselves * Adequate organ and bone marrow function * Participants must be capable of understanding and complying with the protocol requirements and has signed the informed consent document. * Men capable of sexual activity will be required to agree to use a condom during sexual contact with women having the potential to bear children during their participation in the study and for six months after participation. Exclusion Criteria: * Prior therapy with cabozantinib * Any other type of investigational agent within 28 days before the first dose of study treatment or 5 half-lives of the compound or active metabolite, whichever is longer * No radiation therapy within 14 days of study treatment. No radionuclide treatment within two months. * No known brain metastases. * Test results that measure how quickly blood clots need to be adequate for the study * Participants who require concomitant treatment, in therapeutic doses, with anticoagulants such as warfarin or warfarin-related agents, heparin, thrombin or Factor Xa inhibitors, or antiplatelet agents (e.g., clopidogrel). Low dose aspirin (≤ 81 mg/day), low-dose warfarin (≤ 1 mg/day), and prophylactic low molecular weight heparin (LMWH) are permitted. * Participants must not have uncontrolled significant illness including but not limited to: ongoing or active infection requiring systemic treatment, symptomatic congestive heart failure, uncontrolled hypertension , history of hypertensive emergency (e.g.encephalopathy) or hypertensive urgency within 6 months of study treatment, clinically significant wounds including osteonecrosis, history of organ transplant, unstable angina pectoris, stroke within 3 months of study drug, heart attack within 3 months of study drug, development of clots within blood vessels within 6 months of study drug, bleeding from distended veins within 3 months of study drug, any other severe or life threatening hemorrhage/bleeding, major surgery within 4 weeks of study treatment, clinically significant cardiac arrhythmias, history of bowel obstruction within 6 months of study drug or unresolved malabsorption syndrome, untreated bone fracture including tumor-related pathologic fracture, anticipated need for major surgery during the period of the study. * Corrected QT interval, as measured by an ECG, must be within acceptable protocol limits within 28 days of entering the study * Unable to swallow capsules * Unable to undergo MRI * History of another malignant disease within two years with the exception of superficial skin or bladder cancer which has been completely resected or carcinoma in situ without evidence of invasion.