PECAM1 and glioblastoma: One previous study identified protein expression of OATP1A2 and OATP2B1 on human GBM CD31+ vasculature; however, they were unable to detect expression on tumor cells.21 Yet, in this study, all four OATPs investigated were detected at high levels throughout the tumor parenchyma, and the global expression of these proteins were significantly higher in GBM tissue compared to non-tumor tissue.