PTGS2 and endometriosis: Aromatase, a local enzyme, is hyperexpressed in endometriosis, leading to abnormal biosynthesis of estradiol (E2), which in turn, increases PGE2 formation by stimulating COX-2 expression, resulting in a positive feed-forward loop between estrogens and PGs that favors the proliferative and inflammatory characteristics of endometriosis [16,17].