ESR1 and endometrial polyp: In one study, menopausal women with estrogen receptor-positive breast cancer appeared to have a high risk of baseline subclinical endometrial abnormalities.22 Thirty-seven percent of patients had a thickened endometrial stripe and 11%, 4%, and 3% were found to have endometrial polyps, simple hyperplasia, and complex atypical hyperplasia, respectively.