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. The gene discussed is CXCR4; the disease is neoplasm.