MDSCs are mobilized from the bone marrow and recruited into the primary tumor site through various chemo-attractant factors such as M-CSF, GM-CSF, CCL-2 (MCP-1), CCL-5 (RANTES), Bv8 [109,110], which are particularly secreted in hypoxic regions of the tumor (Figure 2) [111]. This evidence concerns the gene PROK2 and neoplasm.