ESR1 and adenoma: In a larger retrospective study, immunostaining for ER-α and progesterone receptors (PR) confirms the expression of one or both receptors in normal mammary gland tissue (75%; 92 of 123 cases) as well as in mammary cysts (68%; 17 of 25 cases), lobular hyperplasia (2 of 2 cases), adenoma (3 of 3 cases) and in situ carcinoma (2 of 2 cases) [11].