Furthermore, ligands and their receptors, such as CXCL12 and CXCR4 (20), tumor-associated exosomes (21), transmembrane proteins, such as CXCR6 (22) and TLR9 (23), protein kinases and related signaling pathways, have already been found to be involved in PCa metastasis. This evidence concerns the gene CXCL12 and neoplasm.