Together, these data demonstrate that, as was seen in cell lines and xenografts, WT1, VEGF, CD31 and MMP9 expression levels in primary Ewing sarcoma tissues are correlated with each other, supportive of the hypothesis that WT1 expression positively regulates tumor angiogenesis by upregulating VEGF and MMP9 expression. Here, PECAM1 is linked to Ewing sarcoma.