Increased levels of COX-2 have been localised in macrophages (Sheehan et al, 2003; Liu et al, 2005), fibroblasts (Sonoshita et al, 2002; Adegboyega et al, 2004) and vascular endothelial cells (VECs) (Brown and DuBois, 2005), indicating that both host and tumour cells may contribute to the production of PGs within the tumour microenvironment and the subsequent development of cancer growth. The gene discussed is PTGS2; the disease is cancer.