CXCR4 and pachyonychia congenita: Although ELR− CXC chemokines belong to the antiangiogenic CXC chemokine family, ELR− CXC chemokines, including CXCR3, CXCR4, CXCR5, CXCR6, and CXCR7, are associated with tumor growth, proliferation, and metastasis in PC (Keeley et al., 2010; Salazar et al., 2013).