In brain metastases from breast cancer, several immunohistochemistry-based studies have shown a strong expression of granulocyte–macrophage colony-stimulating factor (GM-CSF), C-X-C motif chemokine ligand 12 (CXCL12) and its receptor 4 (CXCR4), and CX3CL1. This evidence concerns the gene CXCL12 and breast carcinoma.