It is worth noting that tumor cells injected into tibias still required CXCR4 for Ac-KLF5 to induce bone metastatic lesions (Fig. 8); and CXCR4 was also necessary for the CM from Ac-KLF5 expressing cells to induce osteoclast differentiation (Figs. 4g and 7a), which suggests that CXCR4 might also have a role in paracrine signaling not necessarily related bone homing. The gene discussed is CXCR4; the disease is neoplasm.