Cyclooxygenase 2 (COX-2 / PTGS2/ prostaglandin-endoperoxide synthase 2) is an enzyme involved in the conversion of arachidonic acid to prostaglandin H2, a precursor of prostacyclin that is released during inflammation. Unlike COX1, which is constitutively expressed, COX2 is induced upon inflammation. COX2 is a frequent target for inhibitors (coxibs) to treat inflammatory conditions. Aspirin and nonsteroidal anti-inflammatory agents also inhibit prostaglandin and prostacyclin production by COX2. Overexpression of COX2 also occurs in many cancers, and COX2 inhibitors may assist in preventing the development of colorectal cancers. Staining for COX2 is expected to be cytoplasmic and potentially membranous. In normal tissues, it is expressed in a variety of cells including endothelial cells, smooth muscle cells, cardiac myocytes, the brain and spinal cord, kidney, the GI tract, lung and bladder. References: Biochem Soc Transact 2008 36(3):543; Nat Reviews Drug Discovery 2003 2:179; J Cell Phys 2019 234(5):5683; Gastroenterology 1994 107(4):1183, Curr Med Chem 2000 7(11):1113; PNAS 2016 113(2):434