Cabozantinib (XL184) in Men With Castrate-Resistant Prostate Cancer

• Markers of bone turnover (including BAP and NTx levels) [ Time Frame: Baseline, every 21 days (through Cycle 5) and when participant is removed from the study ] [ Designated as safety issue: No ]
  BAP and NTx levels will be summarized as median (range) and mean (the standard deviation) at baseline and each time point. Percent change from baseline will be summarized overtime.
• Effect on circulating tumor cells categorized as normal versus abnormal [ Time Frame: Baseline, every 21 days (through Cycle 5) and when participant is removed from the study ] [ Designated as safety issue: No ]
  CRC counts assessed by Veridex assay will be categorized as normal versus abnormal. The proportion of patients with abnormal CTC counts will be summarized at baseline and each time point. Change on CTC status from baseline will be tabulated as a two by two contingency table over time.

• Markers of bone turnover (including BAP and NTx levels) [ Time Frame: Baseline, every 21 days (through Cycle 5) and when participant is removed from the study ] [ Designated as safety issue: No ]
  BAP and NTx levels will be summarized as median (range) and mean (the standard deviation) at baseline and each time point. Percent change from baseline will be summarized overtime.
• Effect on circulating tumor cells categorized as normal versus abnormal [ Time Frame: Baseline, every 21 days (through Cycle 5) and when participant is removed from the study ] [ Designated as safety issue: No ]
  CRC counts assessed by Veridex assay will be catergorized as normal versus abnormal. The porportion of patients with abnormal CTC counts will be summarized at baseline and each time point. Change on CTC status from baseline will be tabulated as a two by two contigency table over time.

XL184 is a new drug that is being developed to treat cancer. XL184 works by blocking the "angiogenesis," or the growth of new blood vessels, to the tumor. This is similar to how several other cancer drugs work but in addition XL184 also blocks other pathways that may be responsible for allowing cancer cells to become resistant to these other "anti-angiogenic" treatments. So far XL184 has been investigated in treating brain cancer and a rare form of thyroid cancer. This study will explore lower doses of XL184 with the goal to find the most effective, safe, and tolerable dose without undesirable side effects.

XL184 will be taken by mouth daily. The first five treatment cycles will be 21 days. All cycles after that will be 42 days long. Patients will keep a diary to record study drug dosing.

During the screening phase patients will receive a physical exam, blood and urine tests, a bone scan, a CT of the abdomen and pelvis, and an MRI scan of total body. On Day 1 of each cycle patients will receive a physical exam and blood and urine tests. Bone scan, CT and MRI scans will be performed at the start of cycles 3 and 5, and then repeated once every 12 weeks.

Patients will continue to receive study treatment as long as they are receiving benefit from the treatment, do not experience any severe or unmanageable side effects, and disease does not get any worse.

Inclusion Criteria:

• Histologically confirmed prostate adenocarcinoma
• Bone metastases confirmed by bone scan
• Current androgen deprivation therapy
• Castration-resistant disease based on progression in bone and/or PSA progression
• Recovered from toxicities related to prior treatment, except alopecia, lymphopenia, other non-clinically significant adverse events
• Life expectancy of greater than 3 months
• Normal organ and marrow function
• Capable of understanding and complying with the protocol requirements
• Agree to use medically accepted methods of contraception
• Able to swallow capsules

Exclusion Criteria:

• More than two prior chemotherapy regimens for metastatic prostate cancer
• Known untreated, symptomatic or uncontrolled brain metastases
• Serious or unhealed wound
• Treatment with anticoagulants
• Previously identified allergy or hypersensitivity to components of the study treatment formulation
• History of a different malignancy unless disease-free for at least 5 years, or basal or squamous cell carcinoma of the skin
• Current antiretroviral therapy
• Uncontrolled hypertension
• Uncontrolled intercurrent illness