Modalities include antiestrogens or estrogen blockers such as selective estrogen receptor modulators (SERMs) like tamoxifen, selective estrogen receptor degraders like fulvestrant, and aromatase inhibitors like anastrozole and ovariectomy.
[citation needed] A breast biopsy is tested for whether the cancer cells contain estrogen or progesterone receptors.
[1] ER positive cancers use estrogen to grow, so administering endocrine therapy to a patient diagnosed with ER/PR positive cancer will depress tumor growth.
[2] Estrogen feeds breast cancer cells, so when a woman on hormone replacement therapy (HRT) is diagnosed with ER/PR positive breast cancer, her doctor will ask her to stop the HRT.
Tamoxifen (Nolvadex®) is a commonly used drug for pre-menopausal women diagnosed with ER/PR positive breast cancer.