CXCL12 and central nervous system cancer: Glioma attracts TAMs, especially BMDMs, by secreting chemoattractants, including C-C motif chemokine ligand 2 (CCL2), C-C motif chemokine ligand 3 (CCL3), C-X-C motif chemokine ligand 12 (CXCL12), C-X3-C motif chemokine ligand 1(CX3CL1), colony-stimulating factor 1 (CSF-1), and granulocyte-macrophage colony-stimulating factor (GM-CSF) (30–33).