PTGS2 and urinary bladder carcinoma: Altered metabolism of arachidonic acid, an unsaturated fatty acid, is also a characteristic of tumors, especially those associated with inflammation, such as colorectal cancer, lung cancer and bladder cancer.84 Most of these tumors show increased expression of prostaglandin E2 (PGE2) and cyclooxygenase-2 (COX-2), two key molecules of the arachidonic acid metabolic pathway.