ESR1 and ovarian endometriosis: More cases of low epithelial expression levels of ER-alpha and PR (21.7% and 61.9%, respectively) were observed in samples of ovarian endometriosis, as compared with those of peritoneal endometriosis (0% and 5.9%, respectively) and deep-infiltrating endometriosis (4.3% and 18.2%, respectively; p-value of 0.02 and <0.001).