The G protein-coupled receptor chemokine (C-X-C motif) receptor 4 (CXCR4) is the membrane receptor for the chemokine CXCL12 and was originally identified in peripheral blood leukocytes and other cell types like hematopoietic stem cells, stromal fibroblasts and tumor cells [246,247]. Here, CXCL12 is linked to neoplasm.