Sunitinib treatment induced hypoxia. A-B, representative immunohistochemical preparations stained for pimonidazole to visualize hypoxia and intravital microscopy images of an untreated A-07-GFP tumor (A, left), an A-07-GFP tumor treated with 40 mg/kg/day sunitinib (A, right), an untreated R-18-GFP tumor (B, left), and an R-18-GFP tumor treated with 40 mg/kg/day sunitinib (B, right). Tumor area is delineated by a solid black line in intravital microscopy images. C, hypoxic area fraction for untreated and sunitinib-treated A-07-GFP and R-18-GFP tumors. Points, individual tumors; horizontal lines, mean hypoxic area fraction.