CYP19A1 and endometriosis: Reduced progesterone activity is accompanied by low levels of 17β-hydroxysteroid dehydrogenase (17β-HSD) type 2 production, whereby E2 is not converted to estrone, its biologically less potent metabolite; moreover, in endometriosis tissue there is an high production of p450 aromatase that increases the E2 level [24].