Chemokine (C-X-C motif) receptor type 4 (CXCR4) and its ligand, chemokine (C-X-C motif) ligand type 12 (CXCL12), are relatively highly expressed in invasive breast cancer cells, homing them to distant lymph nodes, the lungs, and the liver [82]. Here, CXCL12 is linked to breast cancer.