CCL2 and cancer: The secreted proteins CCL2 [37, 38], TNFRSF21 [39], PLC [40], COL1A1 [41, 42], PlGF [43, 44], PAI [45, 46] and IL-6 [15, 47] are all known to be involved in cancer progression and have pro-tumorigenic properties, suggesting that cancer cells can be shifted towards a more aggressive state by tumor microenvironmentally induced secretion.