Hormone-Sensitive Breast Cancer

Hormones are substances that function as chemical messengers in the body.  The hormones, estrogen and progesterone, can stimulate the growth of some breast cancers.   These breast cancers are called hormone-sensitive (or hormone-dependent) breast cancers.
Hormone-sensitive breast cancer cells contain proteins known as hormone receptors that become activated when hormones bind to them. The activated receptors cause changes in the expression of specific genes, which can lead to the stimulation of cell growth.
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-negative).
Hormone therapy is used to stop or slow the growth of these tumors.  Therapy is used to treat both early and advanced breast cancer, and to prevent breast cancer in women who are at high risk of developing the disease.
Hormone therapy slows or stops the growth of hormone-sensitive tumors by blocking the body’s ability to produce hormones or by interfering with hormone action.  With that said, tumors that are hormone-insensitive do not respond to hormone therapy.
Hormone therapy for breast cancer is not the same as menopausal hormone therapy, in which hormones are given to reduce the symptoms of menopause.
Several strategies have been developed to treat hormone-sensitive breast cancer, including blocking ovarian function, ovarian ablation, and temporarily suppressing ovarian function by treatment with drugs.  These medicines interfere with signals from the pituitary gland that stimulate the ovaries to produce estrogen.
Drugs called aromatase inhibitors are used to block the activity of an enzyme named aromatase, which the body uses to make estrogen in the ovaries and in other tissues.  Aromatase inhibitors are used primarily in postmenopausal women because the ovaries in premenopausal women produce too much aromatase for the inhibitors to block effectively.   However, these drugs can be used in premenopausal women if they are given together with a drug that suppresses ovarian function.
Several types of drugs interfere with estrogen’s ability to stimulate the growth of breast cancer cells.  Tamoxifen is one of them and has been approved by the FDA.   Tamoxifen has been used for over 30 years to treat hormone receptor-positive breast cancer.
There are three main ways that hormone therapy is used to treat hormone-sensitive breast cancer.   Research has shown that women treated for early-stage ER-positive breast cancer benefit from receiving at least 5 years of adjuvant hormone therapy.
Adjuvant therapy may include radiation therapy, a combination of chemotherapy, and targeted therapy.
Until recently, most women who received adjuvant hormone therapy to reduce the chance of a breast cancer recurrence took tamoxifen every day for 5 years.  However, with the advent of newer hormone therapies, some of which have been compared with tamoxifen in clinical trials, additional approaches to hormone therapy have become common.  For example, some women may take an aromatase inhibitor every day for 5 years, instead of tamoxifen. Other women may receive additional treatment with an aromatase inhibitor after 5 years of tamoxifen.   And, some women may switch to an aromatase inhibitor after 2 or 3 years of tamoxifen, for a total of 5 or more years of hormone therapy.