Tumor-associated macrophages (TAMs), comprising both brain-resident microglia cells and bone marrow-derived macrophages, are recruited by tumor-derived cytokines and chemokines such as CXC motif chemokine ligand 16 (CXCL16), CC motif chemokine ligand 2 (CCL2), transforming growth factor beta (TGF-β) and interleukin 33 (IL-33) [17]. Here, CCL2 is linked to neoplasm.