CXCR4 and breast cancer: Among molecular pathways associated with the breast tumor microenvironment (TME), the C-X-C motif chemokine ligand 12 (CXCL12)/C-X-C chemokine receptor type 4 (CXCR4) axis emerges as a crucial signaling pathway because it induces breast cancer cell motility and is involved in most breast cancer metastases [10,11].