Cyclooxygenase 2 (COX2) expressed in tumour and stromal cells generates prostaglandin E2 (PGE2), which binds to EP2 receptors on cancer cells and promotes tumour cell proliferation and extracellular matrix (ECM) degradation through the expression of matrix metalloproteinase 2 (MMP2) and MMP9 (Ref. 128), a response also elicited by thrombin and SDF1.