CXCL12 and cancer: The C-X-C motif chemokine receptor 4 (CXCR4) in class A is highly expressed in various cancers, including breast, lung and pancreatic cancer and facilitates metastasis through its ligand C-X-C motif chemokine (CXCL12) (Stromal cell-Derived Factor 1-alpha (SDF-1α)) [26–28].