Gliomas help recruit TAMs to the TME by secreting various chemokines, including monocyte chemoattractant proteins (MCP-1/CCL2 and MCP-3) [23], C-X-C motif chemokine 12 (CXCL12) [24], colony-stimulating factor 1 (CSF-1) [25], lysyl oxidase (LOX) [26], and glial cell-derived neurotrophic factor (GDNF) [27] (Figure 1). Here, GDNF is linked to central nervous system cancer.