Endometriosis implants are characterized by increased levels of aromatase and 17β-HSD1, associated with lower levels of 17β-HSD2 (in response to the reduced levels of progesterone receptors), and therefore, an increased level of estradiol is observed in patients with endometriosis, both in the eutopic and ectopic endometrium [2,11]. Here, PGR is linked to endometriosis.