Hormone Therapy for Breast Cancer

You may receive hormone therapy if the cells in your breast cancer contain proteins called hormone receptors. There are two kinds of hormone receptors: estrogen receptors, or ERs, and progesterone receptors, or PRs. To determine whether breast cancer cells contain hormone receptors, doctors test samples of tumor tissue that have been removed by surgery. Learn more about Tests for Breast Cancer Biomarkers.

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

Different types of hormone therapies are used to treat HR-positive breast cancer. Your doctor may suggest one or more types depending on your menopausal status, desire to preserve fertility, and stage of disease.

Therapies that block ovarian function (ovarian ablation)

Because the ovaries are the main source of estrogen before menopause, suppressing ovarian function can reduce or eliminate estrogen in premenopausal women. Blocking ovarian function is called ovarian ablation.

Ovarian ablation can be done surgically, in an operation to remove the ovaries (called oophorectomy), or by treatment with radiation. This type of ovarian ablation is permanent.

Alternatively, ovarian function can be suppressed temporarily with drugs called gonadotropin-releasing hormone (GnRH) agonists. These medicines, which are also known as luteinizing hormone–releasing hormone (LHRH) agonists, interfere with signals that stimulate the ovaries to produce estrogen.

Ovarian suppression drugs used to treat breast cancer include:

• goserelin
• leuprolide

Aromatase inhibitors to block estrogen production

Aromatase inhibitors are used to block the activity of an enzyme called 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, premenopausal women can take aromatase inhibitors if they are given together with a drug that suppresses ovarian function.

Men with advanced breast cancer who are treated with an aromatase inhibitor will also be given a GnRH agonist, such as goserelin or leuprolide.

Aromatase inhibitors used to treat breast cancer include:

• anastrozole
• letrozole
• exemestane

Therapies that block estrogen’s effects

Two types of drugs interfere with estrogen’s ability to stimulate the growth of breast cancer cells:

• Selective estrogen receptor modulators (SERMs) bind to estrogen receptors. In breast cells, SERMs block the effects of estrogen, but in some other cells, such as bone, SERMs act like estrogen. SERMs used to treat breast cancer include:
  • tamoxifen, which is used in both premenopausal and postmenopausal women
  • toremifene, which is used only in postmenopausal women
• Selective estrogen receptor degraders (SERDs), sometimes called pure antiestrogens, bind strongly to estrogen receptors. In addition to blocking the effects of estrogen, they destroy estrogen receptors. Fulvestrant is a SERD approved to treat breast cancer. It is used only in postmenopausal women.

Hormone therapy for HR-positive breast cancer may be given after surgery (also called adjuvant therapy) or before surgery (also called neoadjuvant therapy).

Hormone therapy can also be given if your disease is HR-positive but cannot be treated with surgery, if you’ve had a recurrence, or if you have advanced or metastatic HR-positive breast cancer, meaning it has spread beyond the breast or to distant parts of the body.

Adjuvant therapy for early-stage breast cancer

Your doctor may prescribe hormone therapy after surgery (adjuvant therapy) to reduce your risk of new or recurrent breast cancer. Tamoxifen, aromatase inhibitors, and ovarian suppression may all be used as adjuvant therapy.

Men with early-stage ER-positive breast cancer who receive adjuvant therapy are usually treated first with tamoxifen.

Neoadjuvant therapy for breast cancer

Postmenopausal women with HR-positive breast cancer who cannot take chemotherapy or who cannot have surgery right away may receive hormone therapy with aromatase inhibitors before surgery (neoadjuvant therapy). 

Clinical trials are studying the effectiveness of neoadjuvant hormone therapy for premenopausal women with HR-positive tumors.

Treatment of advanced, metastatic, or recurrent breast cancer

Several types of hormone therapy are approved to treat metastatic HR-positive breast cancer. Hormone therapy is also an option for people with ER-positive breast cancer that has come back in the breast, chest wall, or nearby lymph nodes after treatment (also called a locoregional recurrence).

If you have metastatic or recurrent HR-positive breast cancer, the type of hormone therapy you receive will depend on many factors. Your doctor will suggest a treatment combination tailored to your specific diagnosis. Hormone therapy drugs used to treat metastatic or recurrent HR-positive breast cancer include:

• tamoxifen
• toremifene
• fulvestrant
• anastrozole
• letrozole
• exemestane

Some people with advanced breast cancer are treated with a combination of hormone therapy and targeted therapy. Learn more about Targeted Therapy for Breast Cancer.

The side effects of hormone therapy depend on the specific drug you receive. The most common side effects of hormone therapy are hot flashes, night sweats, and loss of interest in sex. Hormone therapy also may disrupt the menstrual cycle in premenopausal women.

Learn more about the side effects of hormone therapy in both men and women and steps you can take to manage or prevent them at Hormone Therapy to Treat Cancer in the section, "Hormone therapy can cause side effects."

Side effects of hormone therapy can interfere with your life, but many side effects can be relieved by switching therapies or adjusting your dose. One common switching strategy is to take tamoxifen for 2 or 3 years, followed by an aromatase inhibitor for 2 or 3 years.

If side effects are making it difficult for you to continue taking hormone therapy, talk to your doctor about your options. Refusing or stopping hormone therapy is your decision, but research has shown that hormone therapy can effectively lower your risk of new and recurrent breast cancer and of dying from breast cancer.

Researchers have studied hormone therapy as a breast cancer treatment for many decades. Results of studies have shown that hormone therapy, when taken for 5 years or more, can greatly reduce the risk of new breast cancer, breast cancer recurrence, and dying from breast cancer. Your doctor may have information about how effective hormone therapy will be for your specific diagnosis.

Some types of antidepressants can reduce the effectiveness of tamoxifen. This can be an issue because some people with breast cancer have clinical depression and/or hot flashes that are treated with antidepressants.

If you take an antidepressant, talk with your doctor about whether it will reduce the effectiveness of tamoxifen. If so, you may want to discuss switching to a different antidepressant before beginning tamoxifen. Antidepressants that doctors may recommend for people taking tamoxifen include sertraline, citalopram, and venlafaxine.

If you are postmenopausal and taking an antidepressant that reduces tamoxifen’s effectiveness, your doctor may suggest taking an aromatase inhibitor instead of tamoxifen.

Other medications that could interfere with tamoxifen include:

• quinidine, which is used to treat abnormal heart rhythms
• diphenhydramine, which is an antihistamine
• cimetidine, which is used to reduce stomach acid

You should discuss with your doctor all medicines you are currently taking before you start taking tamoxifen.