FOLH1 and glioblastoma: However, as adult GBM’s have shown high tumor-to-background ratios for PSMA radionuclides despite our observation of higher expression in normal brain tissue [17,18,19,20,21,36], we chose to investigate the expression of junctional and transporter proteins known to comprise the neuro-vascular unit (NVU) and regulate the permeability of the blood–brain and blood–tumor barriers (BBB and BTB) [35].