Inclusion Criteria:

- Males and females with histologically confirmed metastatic clear cell RCC

- Measurable disease according to Response Criteria for Solid Tumors (RECIST)

- No prior systemic cytotoxic chemotherapy

- Subjects who have received either no prior therapy for RCC, systemic immunotherapy
only (such as interleukin-2 or interferon), or one agent targeting VEGF or a VEGFR
(eg, bevacizumab, sorafenib, or sunitinib malate) may be enrolled

- ECOG performance status of 0 or 1

- Life expectancy ≥3 months

- Adequate organ and marrow function

- No other malignancies within 5 years

- Signed informed consent

Exclusion Criteria:

- Radiation to ≥25% of bone marrow within 30 days of XL999 treatment

- Subjects who have received systemic anticancer therapy within 30 days of XL999
treatment

- Subjects who have not recovered to grade ≤1 or to within 10% of baseline from adverse
events due to medications administered >30 days prior to study enrollment

- History of or known brain metastases, current spinal cord compression or
carcinomatous meningitis

- Uncontrolled and/or intercurrent illness

- Pregnant or breastfeeding females

- Known HIV