PECAM1 and glioblastoma: In order to identify angiogenic regulators and to discover markers discriminating GBM and surrounding vasculature, we first identified 374 EC-enriched genes by comparing ECs cells with other CD31+ cell types in our data sets, and we subsequently compared the expression of the 374 EC-enriched genes between ECs in tumor core and tumor periphery (Figure 4, B and C, and Supplemental Table 8).