CXCR4 and neoplasm: Prostaglandin E2 (PGE2), catalysed by the enzyme COX-2 is elevated in many tumours (151) and plays a role in tumour evasion by directly inhibiting cytotoxic immune responses and subsequently mediates expression of other inflammatory molecules such as CXCL9, CXCL10, CXCR4, CXCL12, IDO1 and interferon (IFN)-γ (27, 144, 148, 150, 152–154).