Cyclooxygenase (COX-2) is an inducible enzyme involved in production of prostaglandins in inflammatory processes. It is involved in the response of cells to growth factors, tumor promoters, and cytokines that induce its expression. Given its role in synthesizing prostaglandins, COX-2 is therefore of interest in studying immune response regulation. COX-2 is induced by a wide variety of stimuli and was initially identified as immediate-early growth response gene. There is now increasing evidence that a constitutive expression of COX-2 plays a role in development and progression of malignant epithelial tumors. In studies, COX-2 positivity retained independent roles in predicting a poor chance of response to treatment. COX-2 positive patients had a shorter overall survival rate than COX-2 negative patients.