PTGS2 and neoplasm: COX-2 is functionally coupled with mPGES-1 for PGE2 synthesis in pathophysiological conditions,(15) and these enzymes are overexpressed in various tumors and inflammation.(2,15–17) In skin cancers caused by some stimuli such as ultraviolet light and chemicals, COX-2 is induced and PGE2 is increased.(18,19) While COX-2 overexpression certainly induces skin carcinogenesis,(20) studies using COX-2 inhibitor(21) and COX-2 deficient mouse(22) demonstrate the prevention of tumor development in squamous cell carcinoma of the mouse skin.