TEK and neoplasm: In these settings, activation of CXCR4 and CCR2 receptors promote Gi-dependent cell migration.49 Interestingly, the intratumor differentiation of monocyte to macrophage requires CCR2 downregulation to retain the cell in the tumor.166 In cancer patients, populations of Tie2-expressing monocytes/macrophages (TEMs) colonize tumors.