MMP9 and glioblastoma: Looking at the functions reported for the known players, highly expressed MMP9 in GBM contributes to cancer proliferation and progression41,42; CD163 is involved in the regulation of glioma cell stemness and proliferation43; and co-overexpression of CD163 and MMP9 may indicate the polarization of macrophages associated with tumor cells44, supporting their potential to serve as GBM blood markers together.