Analysis of y-z 3D stack of the grade IV glioma vessels revealed that MMRN2 and CD93 were expressed at the abluminal side of the CD31-positive glioblastoma vessels (arrowheads in Supplemental Figure 1, A and B, respectively; supplemental material available online with this article; https://doi.org/10.1172/JCI97459DS1), indicating that the interaction between MMRN2 and CD93 occurs abluminally in proximity to extracellular matrix (arrowheads in Supplemental Figure 1, C and D). Here, PECAM1 is linked to central nervous system cancer.