CXCL12 and breast cancer: Previous studies showed that initial breast cancer bone metastasis occurs via the interaction between soluble cytokines released from the bone microenvironment, especially chemokine (C‐X‐C motif) ligand 12 (CXCL12), and its receptor, C‐X‐C chemokine receptor type 4 (CXCR4) on breast cancer cells, leading to the attraction of breast cancer to bone [3, 4, 5].