Hormone therapy for breast cancer

Hormone therapy is sometimes used to treat breast cancer. It is a treatment that adds, blocks or removes hormones. Hormones are substances that control some body functions, including how cells act and grow. Changing the levels of hormones or blocking certain hormones can slow the growth and spread of breast cancer cells. Drugs, surgery or radiation therapy can be used to change hormone levels or block their effects.

Hormone therapy is only used for breast cancer that is hormone receptor positive. This means that the cancer cells have receptors for estrogen (ER+), progesterone (PR+) or both. When cancer cells have these receptors, the hormones can attach to them and help them grow. Research has shown that giving hormone therapy after surgery and radiation therapy lowers the risk that the breast cancer will come back, and improves survival.

Breast cancer tissue is always tested to find out if it has hormone receptors (called hormone receptor–positive breast cancer) or does not have hormone receptors (called hormone receptor–negative breast cancer). Find out more about hormone receptor status testing.

You may be offered hormone therapy to:

  • lower the risk that non-invasive breast cancer, ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS) may lead to an invasive breast cancer
  • lower the risk that invasive breast cancer can come back (recur) by destroying cancer cells left behind after surgery and radiation therapy (called adjuvant therapy)
  • shrink a large tumour before surgery (called neoadjuvant therapy)
  • treat locally advanced (stage 2B, 3A, 3B or 3C) or recurrent breast cancer
  • relieve pain or control the symptoms of advanced (metastatic) breast cancer (called palliative therapy)

Your doctor will consider your overall health when deciding if hormone therapy is an option for you. Certain health problems may mean that you can’t have certain types of hormone therapy. These problems include thin, brittle bones (called osteoporosis) or a high risk of developing blood clots.

Your doctor will also consider whether or not you have reached menopause and the stage of your cancer when deciding if hormone therapy is an option for you. These factors also affect which hormone therapy drugs they may offer you.

Some women choose not to start hormone therapy right after surgery or chemotherapy. They can still decide to take it after they have finished other treatments. Studies show that taking hormone therapy may still reduce risk of recurrence no matter when you start it.

Hormonal therapy drugs

The 2 most common types of hormonal therapies used to treat breast cancer are anti-estrogen drugs and aromatase inhibitors. If breast cancer stops responding to one type of drug, your doctor may try a different one.

Estrogen receptor blockers

Estrogen receptor blocker drugs attach directly to and block the estrogen receptors on cancer cells so that the cancer cells can’t use estrogen. They do not affect the level of estrogen in the body. Estrogen receptor blockers are also called selective estrogen receptor modulators (SERMs)


Tamoxifen (Nolvadex, Tamofen) is the most commonly used anti-estrogen drug. It is used in post-menopausal and premenopausal women. Tamoxifen is given by mouth (orally) as a pill.

Tamoxifen is the hormonal therapy drug used most often to lower the risk that DCIS or LCIS will lead to an invasive breast cancer.

Tamoxifen very slightly increases the risk for uterine cancer, deep vein thrombosis (DVT) and stroke. Doctors will carefully weigh these risks against the benefits of giving this drug before they offer it to women who have a personal or a strong family history of these conditions. Usually the benefits of taking tamoxifen outweigh these risks.


Fulvestrant (Faslodex) is an anti-estrogen drug that reduces the number of estrogen receptors on breast cancer cells. It is given as an injection into the muscles of the buttocks.

Fulvestrant is used in post-menopausal women if the breast cancer has grown after they were treated with tamoxifen. It is also used in postmenopausal women with locally advanced or metastatic breast cancer that have never been treated with hormonal therapy.

Aromatase inhibitors

Aromatase is an enzyme that the body uses to make estrogen in areas of the body other than the ovaries (such as fat tissue and the adrenal glands). Aromatase inhibitors are drugs that stop the production or block the actions of aromatase, which in turn lowers the level of estrogen in the body.

Aromatase inhibitors are only used in post-menopausal women. After menopause, the ovaries no longer make estrogen, but it is still made by the fat tissue, adrenal gland and other areas of the body. Aromatase inhibitors stop the production of estrogen in these areas of the body, so that there is very little estrogen in the body for the cancer cells to use.

Aromatase inhibitors do not work in premenopausal women because these drugs have no effect on the ovaries, where most of the estrogen in a woman’s body is made before menopause.

Aromatase inhibitors are given as a pill by mouth (orally). The most common aromatase inhibitors offered to treat breast cancer are:

  • letrozole (Femara)
  • anastrozole (Arimidex)
  • exemestane (Aromasin)

Hormonal therapy with aromatase inhibitors can cause bone density loss (called osteoporosis). Your healthcare team will give you supplements to lower the risk of osteoporosis, but some women may need to stop taking the drug because of this side effect.

Ovarian ablation and suppression

Ovarian ablation and suppression are treatments that stop the ovaries from making estrogen. Lowering the level of estrogen in the body can help stop breast cancer cells from growing.

Ovarian ablation leads to permanent menopause and is achieved by either surgery or radiation therapy.

  • Surgical removal of the ovaries (called an oophorectomy) is the preferred method of ovarian ablation in older premenopausal women who no longer wish to have children.
  • Radiation therapy is not a commonly used method of ovarian ablation, but may be offered to women who cannot have surgery. It usually takes about 3 months for the level of estrogen to decrease.

Ovarian suppression uses drugs to lower or stop the ovaries from making estrogen. It causes temporary menopause. These medications are called luteinizing hormone-releasing hormone (LHRH) agonists. The most common LHRH agonists used for ovarian suppression are:

  • goserelin (Zoladex)
  • leuprolide (Lupron, Lupron Depot, Eligard)
  • buserelin (Suprefact)

LHRH agonists are given by an injection under the skin. They are taken for 3 to 5 years.

Adjuvant hormonal therapy for post-menopausal women

Adjuvant hormonal therapy for post-menopausal women includes tamoxifen (an anti-estrogen) and aromatase inhibitors.

You may be offered one of the following options:

  • tamoxifen (Nolvadex, Tamofen) alone for up to 10 years
  • an aromatase inhibitor alone for up to 10 years
  • tamoxifen for 5 years, and then an aromatase inhibitor for up to 5 years (for up to a total of 10 years of hormonal therapy)
  • tamoxifen for 2 to 3 years followed by an aromatase inhibitor for 2 to 3 years, or starting with an aromatase inhibitor followed by tamoxifen, for a total of 5 years of hormonal therapy
  • an aromatase inhibitor for 2 to 3 years, followed by tamoxifen

Adjuvant hormonal therapy for premenopausal women

Adjuvant hormonal therapy options for premenopausal women include tamoxifen for 5 years.

After 5 years, your healthcare team will use blood tests to see if you are in menopause. These tests look for the amount of estrogen or follicle-stimulating hormone (FSH) in your blood. Low estrogen and high FSH levels in your blood mean you are in menopause.

  • If you are still premenopausal, you can continue to take tamoxifen for up to 10 years in total.
  • If you have reached menopause, your healthcare team may offer you the option to continue tamoxifen for up to 10 years in total or to switch to an aromatase inhibitor for up to 5 years (for up to a total of 10 years of hormonal therapy).

For older premenopausal women who no longer wish to have children, the hormonal therapy options include ovarian ablation or suppression, with tamoxifen or an aromatase inhibitor, for up to 10 years.

Side effects

Side effects can happen with any type of treatment for breast cancer, but everyone’s experience is different. Some people have many side effects. Other people have few or none at all.

If you develop side effects, they can develop any time during, immediately after or a few days or weeks after hormonal therapy. Sometimes late side effects develop months or years after hormonal therapy. Most side effects go away on their own or can be treated, but some side effects may last a long time or become permanent.

Side effects of hormonal therapy will depend mainly on the type of hormonal therapy, the dose of a drug or combination of drugs and your overall health. Some common side effects of hormonal therapy for breast cancer are:

Tell your healthcare team if you have these side effects or others that you think might be from hormonal therapy. The sooner you tell them of any problems, the sooner they can suggest ways to help you deal with them.

Information about specific cancer drugs

Details on specific drugs change regularly. Find out more about sources of drug information and where to get details on specific drugs.

Questions to ask about hormonal therapy

Find out more about hormonal therapy and side effects of hormonal therapy. To make the decisions that are right for you, ask your healthcare team questions about hormonal therapy.

Expert review and references

  • American Cancer Society. Breast Cancer. 2015: https://www.cancer.org/.
  • Burstein HJ, Temin S, Anderson H, Buchholz TA, Davidson NE, Gelmon KE, Giordano SH, et al . Adjuvant endocrine therapy for women with hormone receptor-positive breast cancer: American Society of Clinical Oncology clinical practice guideline focused update. Journal of Clinical Oncology. 2014.
  • Drugs and Health Products, Health Canada. Regulatory Decision Summary: Faslodex. 2017: https://hpr-rps.hres.ca/reg-content/regulatory-decision-summary-detail.php?linkID=RDS00452.
  • Eisen A, Fletcher GG, Gandhi S, Mates M, Freedman OC, Dent SF, Trudeau ME and members of the Early Breast Cancer Systemic Therapy Consensus Panel . Optimal systemic therapy for early breast cancer in women: a clinical practice guideline. Current Oncology. 2015.
  • Goss, PE, Ingle JN, Pritchard KJ, et al . Extending aromatase-inhibitor adjuvant therapy to 10 years. New England Journal of Medicine. 2016.
  • Joy AA, Ghosh M, Fernandes R, Clemons MJ . Systemic treatment approaches in HER2-negative advanced breast cancer - guidance on the guidelines. Current Oncology. 2015.
  • Morrow M, Burstein HJ, and Harris JR . Malignant tumors of the breast. DeVita VT Jr, Lawrence TS, & Rosenberg SA. Cancer: Principles and Practice of Oncology. 10th ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins; 2015: 79: 1117-1156.
  • National Cancer Institute. Breast Cancer Treatment for Health Professionals (PDQ®). 2015.
  • National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Breast Cancer (Version 2.2015). http://www.nccn.org/professionals/physician_gls/f_guidelines.asp.

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