PTGS2 and neoplasm: Cyclooxygenases (COX-1 and COX-2) convert arachidonic acid toprostaglandin H2(PGH2), an endoperoxide intermediatethat, via specific synthases, is then transformed to prostaglandins (PGE2, PGD2, PGF2α, PGI2) and thromboxanes (TXA2).Whereas COX-1 is constitutively expressed in most tissues, COX-2 is transcriptionally upregulated in response tomitogens, tumor promoters, and pro inflammatory stimuli in a discretenumber of cell types (reviewed in [77–79]).