CXCL1 and neoplasm: Tumor-derived CXCR2-ligands (IL-8, CXCL1, CXCL2, and CXCL5) attract MDSCs to the tumor microenvironment [71–73] and inhibition of CXCR2 profoundly suppresses Gr-1+ leukocyte migration into tumor [74].