A: Functional vessel density, time course. Y-axis: functional vessel density (FVD in mm/mm2), x-axis: time in days after tumor implantation. SU6668 induced a regression of functional vessel density (FVD), while FVD in Controls increased between day 7 and 14 after tumor implantation, remaining constant thereafter. B: Tumor surface, time course. Y-axis: tumor surface (ATUM in mm2), x-axis: time in days after tumor implantation. In Controls, tumor surface continuously increased over the period of investigation. In contrast to this, SU6668 induced a growth arrest of chondrosarcomas beginning on day 14 after tumor implantation. A and B: Treatment started on day 7 after tumor implantation. Results are given as median with 25% quartiles and 75 % quartiles. Mann-Whitney rank sum test, #p < 0.05 versus Control, *p < 0.05 versus day 7 after tumor implantation. C and D: Immunohistochemistry for CD31 (PECAM-1) on day 28 after tumor implantation confirmed the results of the in vivo quantification of the functional vessel density with intravital microscopy. Untreated Controls showed uniformly distributed CD31 positive cells (brown) within the implanted tumors (C). In SU6668 treated tumors, CD31 positive cells were rare and only detectable in peripheral areas of the tumor residues (D). Scale bars represent 50 μm.