CXCL12 and breast cancer: Particularly, different growth factors and cytokines released by stromal cells and breast cancer cells, including SDF-1, TGF-β1 and BMPs as well as the up-regulation of HIF-1α, NF-κB, vascular cell adhesion molecule-1 (VCAM-1) and Notch in breast cancer cells typically control their dormancy, survival and self-renewal ability and formation of osteolytic bone metastasis [1, 15, 239, 251, 254, 258–261].