Among the proteins identified, there were many typical serum proteins, like albumin and immunoglobulins, that, even under normal conditions, enter CSF from plasma but also prostaglandin-H2 D-isomerase, the second most abundant protein in CSF [33], which is predominantly produced by arachnoid cells and oligodendrocytes [34] and appears upregulated in the CSF of gliomas and high-grade meningiomas [35]. Here, PTGDS is linked to glioma.