Tumor cells initiate recruitment of monocyte-derived circulating macrophages by production of Colony Stimulating Factor 1 (CSF1) and CC chemokine Ligand 2 (CCL2), leading to their binding to CSF1 receptor (CSF1R) and CCL2 receptor (CCR2) on the macrophage cell surface. The gene discussed is CSF1; the disease is neoplasm.