What is hormone therapy?

Hormone therapy is used to treat breast cancer that is hormone-receptor positive, meaning it is fueled by certain hormones in your body. About 70% of all breast cancers are hormone-positive. Breast cancer cells can have receptors for the hormone estrogen (this is called ER positive breast cancer) and/or receptors for another hormone called progesterone (PR positive breast cancer). When these hormones attach to these receptors, particularly estrogen, the cancer cells are stimulated to grow and divide.

There are different types of hormone therapy that work by either blocking or lowering levels of estrogen to slow or stop the growth of breast cancer. The type of hormone therapy suggested would depend on whether you are premenopausal or post menopausal.

Hormone therapy for breast cancer may also be referred to as hormonal or anti-estrogen therapy. It is important to note that this type of hormone therapy is not the same as hormone therapy used to treat menopausal symptoms (also known as hormone replacement therapy or HRT).

What are the types of hormone therapy?

Estrogen receptor blockers 

Tamoxifen may be recommended to both premenopausal and postmenopausal women whose breast cancer is hormone receptor positive. It is the most commonly used estrogen receptor blocker and it belongs to a class of drug called Selective estrogen receptor modulators (SERMs). It acts by attaching to the estrogen receptors on breast cancer cells thereby blocking the body’s own estrogen from attaching.

Aromatase inhibitors

Aromatase inhibitors (AIs) are given to postmenopausal women only. After menopause, the ovaries stop making estrogen, but low levels of estrogen are still being made by a rather complex process involving the enzyme aromatase which can be found in fat, muscle, liver and breast tissues. AIs stop or inhibit aromatase from working, resulting in lowered levels of estrogen in the body. AIs that may be recommended to you include Arimidex (chemical name: anastrozole), Aromasin (exemestane) or Femara (letrozole).

Ovarian Suppression and Luteinizing hormone-releasing hormone (LHRH) agonists

In premenopausal women, the ovaries produce most of the estrogen in the body. For some young women suppressing the ovaries may be recommended to decrease estrogen to postmenopausal levels. This can be done by surgically removing the ovaries (oophorectomy) or by treating them with radiation that will put women into permanent menopause. It is also possible to use drugs called LHRH agonists, such as Zoladex (goserelin) or Lupron (leuprolide) which will put women in a reversible menopause.

How and when is hormone therapy given?

Tamoxifen and AIs are pills taken orally once a day. You will be given a prescription so that you can take the pills at home. Tamoxifen is usually taken for 5 years, however new research is showing that some women may benefit from an additional 5 years of treatment.

Postmenopausal women are prescribed AIs for 5 years. An AI may also be prescribed after 5 years of Tamoxifen to further reduce the risk of a breast cancer recurrence. Research in ongoing to determine the ideal length of time that one should take an AI.

Zoladex or Lupron, which temporarily shut down the ovaries, may be given as injections once a month for several months or every few months.

What are the side effects?

Women taking hormone therapy may have symptoms similar to those experienced during menopause, as a result of having low body levels of estrogen. Common side effects of all hormone therapy are hot flashes, night sweats and vaginal dryness. Side effects of Tamoxifen can also include fatigue, nausea, mood swings, depressions, and vaginal discharge. Rare side effects are blood clots, endometrial cancer and stroke. Side effects of aromatase inhibitors can also include bone and joint pain, mood swings and depression, increased risk of fractures and osteoporosis, and heart issues.

Links to more information

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Hormonal Therapy for Early-Stage Hormone Receptor-Positive Breast Cancer
American Society of Clinical Oncology (ASCO)

Hormonal Therapy

Hormone Therapy for Breast Cancer
National Cancer Institute

Hormone Therapies
Susan G. Komen for the Cure

Hormonal Therapies for Breast Cancer
Macmillan Cancer Support

Types of Breast Cancer Hormonal Therapy
Cancer Help UK

Hormone Therapy
Breast Cancer Care UK