CCR2 and neoplasm: Studies have shown that adrenergic stimulation upregulates C-C motif chemokine ligand 2 (CCL2) of lung stromal cells and C-C motif chemokine receptor 2 (CCR2) of monocytes, which results in macrophage recruitment and infiltration into the pre-metastatic lung and promote lung metastatic colonization of circulating tumor cells [33, 34].