PTGS2 and cancer: Overproduction of COX-2 and its major metabolite prostaglandin E2 (PGE2) has been found in many human cancers, including colorectal tumours (Rigas et al, 1993; Eberhart et al, 1994; Sano et al, 1995), with COX-2 levels increased in about 90% of colon cancers and ∼50% of pre-malignant colorectal adenomas (Eberhart et al, 1994).