PECAM1 and glioblastoma: To determine if this macrophage network is present in human tumors, we performed immunohistochemical analysis for the macrophage marker CD163 and the ‘endothelial’ marker CD31 on human tissue specimens from 5 skin melanomas, 2 spinal schwannomas, 1 cerebellar hemangioblastoma, 3 meningiomas (1 malignant WHO grade 3, 2 benign WHO grade 1), and 2 glioblastomas.