Abstract： Objective To investigate the effect and associated mechanism of high-intensity focused ultrasound ablation on metastasis in infant SD rat bearing human neuroblastoma.Methods 120 Infant SD rats bearing human neuroblastoma were divided into two groups(60/group)at random:HIFU-treatment group and surgery group,and 60 Infant SD rats as normal control group.At 3,14,28 days after treatment,central tissues (tumor tissues by HIFU ablation),marginal tissues(skin and muscle tissues),and other adjacent organs were examined by gross anatomy and light microscope with HE stain.On day 0 before treatment,3,14 and 28 days after treatment,the expression of VEGF and T lymphocyte subsets in peripheral blood were detected by ELISA and flow cytometry.Results (1)Through gross anatomy and light microscopy with HE stain,when compared with the surgery group,there was a significant decrease of metastatic rate in HIFU-treatment group(P＜0.05).(2) There was a significant decrease of serum-VEGF concentrations in infancy SD rats bearing human neuroblastoma after HIFU treatment compared with pre-treatment,and the levels in the HIFU group were lower than those in the surgery group (P＜0.01).There was a decreasing tendency of serum-VEGF concentration in SD rats after surgery compared with those before treatment,but the significant decrease was seen only on day14 (P＜0.05).(3) The results showed a significant increase in the peripheral blood levels of CD3 + 、CD4 + lymphocytes and the ratios of CD4 +/CD8 + and a significant decrease of CD8 + level in infant SD rats bearing human neuroblastoma after HIFU treatment (P＜0.05).However,no statistical differences were found pre-and postoperatively (P＞0.05).Compared to the values in surgery group,there was a significant increase of CD3 + 、CD4 + level and CD4 + /CD8 + ratios(P＜0.05),and a significant decrease of CD8 + level in HIFU-treatment group and normal control group after treatment.(P＜0.05).There was no significant difference between HIFU-treatment group and normal control group on day 14 and day 28 after treatment (P＞0.05).Conclusions High-intensity focused ultrasound ablation can inhibit the tumor metastasis through suppressed expression of VEGF in the peripheral blood and improve cell-mediated immune function in the infant SD rats bearing human neuroblastoma.