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About estrogen and progesterone receptors
Estrogen receptors (ER) and progesterone receptors (PR; also called PgR) may be found in breast cancer cells. Cancer cells with these receptors depend on estrogen and related hormones, such as progesterone, to grow. Estrogen and progesterone influence many hormonal functions in women, such as breast development.
If breast cancer cells have estrogen receptors, the cancer is called ER-positive breast cancer. If breast cancer cells have progesterone receptors, the cancer is called PR-positive breast cancer. If the cells do not have either of these two receptors, the cancer is called ER/PR-negative. About two-thirds of breast cancers are ER and/or PR positive.
About hormone therapy
Learning whether a tumor has estrogen and/or progesterone receptors helps doctors determine a patient's risk of recurrence (return of the cancer after treatment) and whether the cancer can be treated with hormone therapy. Hormone therapy blocks the tumor from using estrogen and/or progesterone for cancers that are ER and/or PR positive, slowing or stopping tumor growth. Two types of drugs may be used; one type called tamoxifen (Nolvadex) can be used for women of all ages, while other types of drugs called aromatase inhibitors (AIs) stop tissues and organs other than the ovaries from producing estrogen. AIs must never be used alone for women who have not gone through menopause.
For women who have not gone through menopause, hormone therapy for ER and/or PR positive tumors may include stopping the production of estrogen and progesterone in the ovaries with surgery or injections.
Testing estrogen and progesterone receptors
Testing the tumor for both estrogen and progesterone receptors is a standard part of a breast cancer diagnosis. Because the results are used to guide treatment, it's important that the results be accurate. The most common method currently used to test a tumor for estrogen and progesterone receptors is called immunohistochemistry or IHC. IHC testing can detect estrogen and progesterone receptors in cancer cells from a sample of tissue. This tissue may come from a biopsy (removal of a small amount of tissue for examination under a microscope), or from the surgery to remove all of the tumor and some or all of the breast.