PTGS2 and endometriosis: Previous studies have revealed that both estrogen (E2) and prostaglandin E2 (PGE2) are crucial factors for the development of endometriosis [21, 172] and the enzymes control the rate limiting steps of E2 (aromatase and steroidogenic acute regulatory protein, StAR) and PGE2 (cyclooxygenase-2, COX-2) biogenesis are aberrantly expressed in endometriotic stromal cells [9, 55, 153, 173].