CXCL12 and pachyonychia congenita: Chemokine (C-X-C motif) receptor 4 (CXCR4) expression increases during progression of PCa and is associated with metastatic disease and poor survival [50, 51] CXCR4 selectively binds to stromal cell-derived factor 1 (SDF-1)/ CXCL12, also overexpressed in PC metastatic tissue compared to normal tissues [52].