The nine proteins selected in this study are brain-enriched secretory proteins that are differentially regulated in GBM and involved in oncogenic pathways involved in GBM development, i.e., opioid binding protein/cell adhesion molecule-like (OPCML), neuronal pentraxin 1 (NPTX1), contactin 2 (CNTN2), leucine-rich glioma-inactivated 1 (LGI1), lymphocyte antigen 6 family member H (LY6H), slit guidance ligand 1 (SLIT1), growth differentiation factor 1 (GDF1), cellular repressor of E1A-stimulated genes 2 (CREG2) and serine proteinase inhibitor 1 (SERPINI1). Here, GDF1 is linked to glioblastoma.