The recruitment of these MDSC subtypes to tumor sites is mediated by chemokines highly expressed by tumor-associated neutrophils, including CXCR2 and CXCR4, and chemokines over-expressed by tumor infiltrating macrophages, including CCR2, CCR5, CXCR4 and CX3CR1 [5]. This evidence concerns the gene CXCR4 and neoplasm.