Hormone therapy (also called hormonal therapy, hormone treatment, or endocrine therapy) slows or stops the growth of hormone-sensitive tumors by blocking the body’s ability to produce hormones or by interfering with effects of hormones on breast cancer cells. Tumors that are hormone insensitive do not have hormone receptors and do not respond to hormone therapy.
To determine whether breast cancer cells contain hormone receptors, doctors test samples of tumor tissue that have been removed by surgery. If the tumor cells contain estrogen receptors, the cancer is called estrogen receptor positive (ER positive), estrogen sensitive, or estrogen responsive. Similarly, if the tumor cells contain progesterone receptors, the cancer is called progesterone receptor positive (PR or PgR positive). Approximately 80% of breast cancers are ER positive (1). Most ER-positive breast cancers are also PR positive. Breast tumors that contain estrogen and/or progesterone receptors are sometimes called hormone receptorpositive (HR positive).
Breast cancers that lack estrogen receptors are called estrogen receptor negative (ER negative). These tumors are estrogen insensitive, meaning that they do not use estrogen to grow. Breast tumors that lack progesterone receptors are called progesterone receptor negative (PR or PgR negative). Breast tumors that lack both estrogen and progesterone receptors are sometimes called hormone receptor negative (HR negative).
Hormone therapy for breast cancer should not be confused with menopausal hormone therapy (MHT)—treatment with estrogen alone or in combination with progesterone to help relieve symptoms of menopause. These two types of therapy produce opposite effects: hormone therapy for breast cancer blocks the growth of HR-positive breast cancer, whereas MHT can stimulate the growth of HR-positive breast cancer. For this reason, when a woman taking MHT is diagnosed with HR-positive breast cancer she is usually asked to stop that therapy.
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