Taken together with the results of Fig. 4, it is likely that CXCL12/CXCR4 signaling plays a key role in the initial establishment of prostate tumors in the bone; however, the importance of CXCL12/CXCR4 appears to be taken over by other signaling mechanisms during the enlargement phase of bone tumors. This evidence concerns the gene CXCR4 and bone neoplasm.