Tumor angiogenesis is a critical factor for tumor growth, and MVD is an important parameter for assessing angiogenesis in tumors (14, 15). Subsequently, we quantified the effect of combination of SDRT and Pazopanib on tumor MVD. Figure 2C and 2D show that Pazopanib alone reduced MVD to 56.2% ± 14.5% (vs control) in JJ012 tumors and to 79.5% ± 10.8% (vs control) in MPNST3 tumors. Whereas SDRT alone caused a decrease in MVD in JJ012 to 68.8 ± 23.3% (vs control) and to 84.6 ± 16.8% (vs control) in MPNST3, the combination of SDRT and Pazopanib showed an enhanced decrease in MVD in JJ012 (34 ± 11.8%, vs control) and MPNST3 (62.3 ± 11.8%, vs control). These results indicate that Pazopanib enhances SDRT effect on tumor growth delay by significantly increasing SDRT-induced TEC apoptosis and reducing angiogenesis in these tumors.