CXCL12 and neoplasm: As with other chemokine receptors, CXCR7 belongs to the superfamily ofseven-transmembrane (7TM) G protein coupled receptors, though current evidenceindicates that CXCR7 does not stimulate typical G protein-dependent pathways, andmay act as a β -arrestin-biased receptor [7]–[9] and/or as a chemokine scavenger,particularly during development or in the tumor microenvironment – i.e.sequestration of CXCL12 by binding to CXCR7 may help create a CXCL12 gradient in theextracellular space, resulting in proper chemotaxis/migration of CXCR4-expressingcells [8], [10], [11].