Subsequently, irradiation with 30 Gy combined with Pazopanib pretreatment of MPNST3 tumors resulted in 50% decrease in perfusion in the tumors 30 minutes post SDRT, compared to untreated tumors (Figure 3, p < 0.01). Treatment with 15 Gy or 30 Gy with Pazopanib and Pazopanib alone caused a 30% decrease. Radiation alone did not cause a decrease in perfusion in this tumor model. These results indicate that the improved tumor growth delay in response to combination of Pazopanib and SDRT treatment are due to enhanced microvascular dysfunction generated by this combination treatment in these sarcoma tumor models. Similar results were obtained in pre-clinical mouse tumor models using SDRT in which the perfusion reduction was accompanied by secretion of ASMase into the systemic circulation within the first hour of radiation (Campagne and Fuks submitted publication).