CXCR4 and cancer: CXCR4, a G-protein coupled receptor (GPCR) [59], is one of the most ubiquitously overexpressed chemokine receptors in diverse cancers and in conjunction with its primary chemokine ligand, CXCL12 (also known as stromal-derived factor-1, SDF-1), impacts several hallmarks of cancer including resistance to apoptosis, sustaining proliferative signals, angiogenesis, evading growth suppression, replicative immortality, and invasion and metastasis [58].