In a study looking at mouse models of breast, colon, and liver tumors, knockout of HIF-1α and HIF-2α decreased tumor growth, but only HIF-2α knockout lead to decreased expression of macrophage colony-stimulating factor receptor (M-CSFR) and CXCR4 on tumor-infiltrating macrophages [145]. The gene discussed is CXCR4; the disease is neoplasm.