Hormone Therapy for Breast Cancer

Some breast cancers use hormones to grow. Hormone therapy slows or stops the growth of these tumors. It is also called hormonal therapy, hormone treatment, or endocrine therapy. It works in two ways. It can block the body's ability to make hormones. Or it can get in the way of what hormones do to breast cancer cells.

Hormone therapy works against breast cancers that rely on hormones to grow.

You may get hormone therapy if your breast cancer cells contain proteins called hormone receptors. There are two kinds: estrogen receptors (ERs) and progesterone receptors (PRs). To find out, doctors test tumor tissue removed by surgery.

Say the tumor cells do contain hormone receptors. Then the cancer is called hormone receptor positive (HR positive). Tumors that lack them are HR negative. They do not respond to hormone therapy. About 80% of people diagnosed with breast cancer have HR-positive cancers.

Hormone therapy for breast cancer is not the same as menopausal hormone therapy.

Your doctor may suggest one type or more. The choice depends on your menopausal status, your wish to preserve fertility, and the stage of the disease.

Therapies that block ovarian function. Before menopause, the ovaries are the main source of estrogen. Blocking ovarian function, called ovarian ablation, can lower or remove estrogen. Surgery or radiation does this for good. Drugs can do it for a time. They block the signals that tell the ovaries to make estrogen.

Aromatase inhibitors. These block an enzyme called aromatase. The body uses it to make estrogen. These drugs are used mainly in postmenopausal women. Premenopausal women can take them too. They add a drug that suppresses ovarian function.

Therapies that block estrogen's effects. Two kinds of drugs get in the way of estrogen fueling cancer growth:

• Selective estrogen receptor modulators (SERMs) bind to estrogen receptors. In breast cells, they block what estrogen does. Tamoxifen is used in both premenopausal and postmenopausal women. Toremifene is used only in postmenopausal women.
• Selective estrogen receptor degraders (SERDs) bind strongly to estrogen receptors and destroy them as well. Fulvestrant is a SERD used only in postmenopausal women.

Hormone therapy for HR-positive breast cancer may be given after surgery. That is called adjuvant therapy. It may also be given before surgery, which is neoadjuvant therapy. It can be used when your disease is HR positive but surgery is not an option. It can be used if the cancer has come back. And it is used if the cancer is advanced or metastatic, meaning it has spread to other parts of the body.

• Adjuvant therapy for early-stage cancer. After surgery, hormone therapy can lower your risk of new or returning breast cancer. Tamoxifen, aromatase inhibitors, and ovarian suppression may all be used.
• Neoadjuvant therapy. Some postmenopausal women cannot take chemotherapy, or cannot have surgery right away. They may get aromatase inhibitors before surgery.
• Advanced, metastatic, or recurrent cancer. Several types of hormone therapy are approved here. Some people get hormone therapy plus targeted therapy.

Side effects depend on the drug. The most common are hot flashes, night sweats, and loss of interest in sex. Hormone therapy may also upset the monthly cycle in premenopausal women.

If side effects get in the way of your life, many can be eased. Switching drugs or changing your dose often helps. One common approach is to take tamoxifen for 2 or 3 years, then switch to an aromatase inhibitor. Stopping or refusing hormone therapy is your decision. But research shows it can lower your risk of new and returning breast cancer, and of dying from breast cancer.

Studies over many decades back this up. Taken for 5 years or more, hormone therapy can greatly cut the risk of a new breast cancer. It also cuts recurrence and death from breast cancer. Some medicines can make tamoxifen work less well, including certain antidepressants. So tell your doctor about every medicine and supplement you take.

Taken over several years, hormone therapy can clearly lower the chance that HR-positive breast cancer returns.

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• Call your care team the same day if one calf turns swollen, red, or tender to press. Call the same day too if you have vaginal bleeding that is not your usual period.
• Call your care team within a day or two if vaginal discharge turns bloody, brown, or rusty, if pelvic pressure settles in and stays, or if your eyesight changes.

Sources: MedlinePlus: tamoxifen and American Cancer Society: hormone therapy for breast cancer.