CCL2 and neoplasm: The phenomenon that PGE2 potentiates the production of CCL2 and simultaneously reduces CXCL8 production by GM-CSF/IL-6 M-MDSC, could explain the observation that M-MDSC accumulate preferentially in PGE2-rich tumor site, rather than PMN-MDSC (3, 11), although this hypothesis needs to be tested independently.