In bone metastases, osteoblasts in the bone marrow can attract CTCs using chemoattractants like ligand stromal cell-derived factor-1 (SDF-1) or C-X-C motif chemokine 12 (CXCL12), which binds to C-X-C motif receptor 4 (CXCR4) receptors highly expressed in breast cancer cells. This evidence concerns the gene CXCL12 and breast carcinoma.