CXCL12 and neoplasm: Many cytokines secreted by tumor cells can recruit macrophages to the TME, but some of them are exclusively produced by CSCs: CCL2, CCL3, CCL5, CXC motif chemokine ligand 12 (CXCL12), olfactomedin-like 3 (OLFML3), stromal-cell-derived factor-1b (Sdf1b), IL-6, IL-33, and CSF-1 [37,38,39,40,41,42,43,44,45] (Figure 1).