Considering the relatively low cell numbers of ECs, consisting of typically 5 to 10% of total nonneoplastic cells, ECs may not be the main source for OPN, but infiltrating monocytes/macrophages are educated by locally enriched OPN in the vascular niche, serving as a major driving force for M2-like Mφ polarization and GBM immunosuppression. Here, SPP1 is linked to glioblastoma.