Various chemokines and cytokines promote macrophage recruitment to tumor tissues, such as C-C motif chemokine ligand 2 (CCL2), macrophage colony-stimulating factor (GM-CSF), VEGF, CXCL-12 and hypoxia-inducible factors (HIFs) (Tang et al., 2013; Cassetta and Pollard, 2018). The gene discussed is CXCL12; the disease is neoplasm.