CXCR4 and cancer: It has been established that bone metastatic cells can express chemokine receptor 4 (CXCR4) that provokes actin polymerization and pseudopodia formation resulting in migration upon exposure to bone endothelial cell secretions; thus, CXCR-4 enables circulating cancer cells to migrate into bone tissue to form the pre-metastatic niche [56].