What is the reason we give antiestrogen drugs to post-menopausal women who have breast cancer ?

Astute question!!: Post menopausal women and women who had their ovaries removed still produce sex steroids in the adrenal glands that are later converted to estrogen. Cancer cells learn how to function with those minute quantities of Estrogens and for that reason we target the estrogen receptor pathway in these women. Thank you for that good question.