Axitinib-13C-d3 is intended for use as an internal standard for the quantification of axitinib by GC- or LC-MS. Axitinib is a VEGFR inhibitor (IC50s = 1.2, 0.25, and 0.29 nM for VEGFR1, -2, and -3, respectively). It also inhibits c-Kit and PDGFRβ (IC50s = 1.7 and 1.6 nM, respectively). It inhibits VEGF-induced migration of and tube formation by human umbilical vein endothelial cells (HUVECs). Axitinib (1-100 mg/kg) reduces microvessel density, a marker of angiogenesis, and tumor growth in MV522 colon carcinoma, A375 melanoma, SN12C-GFP renal carcinoma, and U87 glioma mouse xenograft models in a dose-dependent manner. Formulations containing axitinib have been used in the treatment of renal cell carcinoma.