Sunitinib is a small molecule that inhibits multiple receptor tyrosine kinases (RTKs), some of which are involved in tumor growth, pathological angiogenesis, and metastatic progression of cancer. Sunitinib was evaluated for its inhibitory activity against a variety of kinases (>80 kinases) and was identified as a platelet-derived growth factor receptor (PDGFRα and PDGFRβ), vascular endothelial growth factor receptors (VEGFR1, VEGFR2, and VEGFR3), stem cell factor receptor (KIT), Fms-like tyrosine kinase-3 (FLT3), colony-stimulating factor receptor type 1 (CSF-1R), and glial cell line neurotrophic factor receptor (RET). Inhibition of the activity of these RTKs by sunitinib was demonstrated in biochemical and cellular assays, and inhibition of function was demonstrated in cell proliferation assays. The major metabolite demonstrates similar efficacy compared to sunitinib in biochemical and cellular assays.