CASP3 and neoplasm: In an attempt to define whether the observed effects of sunitinib on ccRCC xenograft volume were due to its inhibitory actions on tumor growth and vascularization (40), sunitinib-treated xenografts were stained for caspase 3, a marker of apoptosis, and CAIX, a commonly used marker of hypoxia, which was found to be upregulated in response to anti-angiogenic agents (47, 48).