CXCL12 and glioblastoma: The recruitment and function of TAMs is modulated by GBM-secreted factors, such as the chemo-attractants stromal cell-derived factor 1 (SDF1) (47, 48), C–C motif chemokine ligand 2 (CCL2) (49, 50) and the colony-stimulation factor 1 (CSF1) (51).