PECAM1 and glioblastoma: While both CD31 and CD34 labelling may be used in combination with PAS staining to distinguish VM vessels (PAS+/CD31- or PAS+/CD34-) from endothelial vessels (PAS+/CD31+ or PAS+/CD34+), the majority of studies that assessed VM in glioblastoma using IHC confirmed the lack of endothelial lining by labelling tissue for CD34.