Cancer is a worldwide clinical and economic problem. Conventional approaches to treating cancer include surgery, radiotherapy, and cytotoxic chemotherapy as single modalities or as combined therapies. Recently, targeted therapies including antibodies and small molecule inhibitors have also demonstrated clinical benefit. It is now possible to study different genetic lesions involved in cancer types due to advances in genomic methodologies. The investigational drug in this study, XL999 inhibits multiple receptor tyrosine kinases, including VEGF receptor (VEGFR2/KDR), platelet derived growth factor receptors (PDGFRβ), fms-like tyrosine kinase receptor 3 (FLT3), fibroblast growth factor receptors (FGFR1, FGFR3), RET, and KIT, and thus, interferes with multiple cellular processes simultaneously and will likely have effects on the integrity of tumor neovasculature and angiogenesis. Together with the ability to induce a novel cell cycle arrest, the spectrum of activities that XL999 exhibits may reduce both tumor cell proliferation and angiogenesis in the clinic.

The rationale and purpose of this maintenance study is to allow a subject receiving clinical benefit from XL999 to continue treatment.

Inclusion Criteria:

• The subject is eligible to continue to receive XL999 in the absence of progressive disease and unacceptable XL999-related toxicity.

Exclusion Criteria:

• Progressive disease.