PTGS2 and cancer: The possible mechanisms of low expression of HPGD promoting cancer progression are listed as follows: firstly, HPGD, the prostaglandin E2 (PGE2) metabolizing enzyme, is the key enzyme that regulates prostaglandins (PGs) level by converting them to the corresponding 15-keto derivatives; so it is responsible for the biological inactivation of PGs [14], which are implicated in the initiation and progression of many malignancies [15, 16]; secondly, HPGD has the ability to antagonize the effects of cyclooxygenase-2 (COX-2) and also inhibits angiogenesis in vivo.