Hormone therapy for breast cancer

Hormones are substances that control some body functions, including how cells act and grow. Hormone therapy adds, blocks or removes hormones to slow or stop the growth of cancer cells that need hormones to grow. Hormone levels can be changed or blocked by drugs, surgery or radiation therapy. Hormone therapy is also called endocrine therapy.

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.

Hormone therapy is only used for breast cancer that is hormone-receptor positive. This means that the cancer cells have receptors for estrogen (estrogen-receptor positive, or ER+) or progesterone (progesterone-receptor positive, or PR+) or both. When cancer cells have these receptors, these hormones can attach to them and help them grow. Hormone therapy therapy stops the hormones from attaching to the cancer cells. The cells then "starve" and die. This lowers the risk that breast cancer will come back and improves survival.

Most people with breast cancer have hormone therapy because most breast cancers are hormone-receptor positive.

Hormone therapy may be used along with other cancer treatments, or it may be the only treatment you have. You may have hormone therapy to:

• lower the risk of developing a second breast cancer
• lower the risk of recurrence of ductal carcinoma in situ (DCIS) or an invasive breast cancer after breast-conserving surgery and radiation therapy
• lower the risk of breast cancer in parts of the body other than the breast and lymph nodes (called adjuvant therapy)
• treat pleomorphic lobular carcinoma in situ
• shrink a large tumour so it can be removed more easily with breast-conserving surgery (called neoadjuvant therapy)
• treat locally advanced or recurrent breast cancer
• shrink tumours and control the symptoms of advanced (metastatic) breast cancer (called palliative therapy)

If you have certain health problems, it 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.

The most common hormone therapy drugs used to treat ER+ breast cancer are tamoxifen and aromatase inhibitors (AIs).

Tamoxifen is a type of drug called an estrogen receptor blocker. These drugs stop or block estrogen in the body from attaching to ER+ breast cancer cells. When the cancer cells can't get the hormones, the tumour growth may slow and the cells may die. Estrogen receptor blockers do not stop estrogen from being made in the body – they only stop estrogen from attaching to breast cancer cells. Since tamoxifen only targets the estrogen receptors found on breast cancer cells, it is also called a selective estrogen receptor modulator (SERM).

Tamoxifen is given as a pill. It is used for both premenopausal and post-menopausal people. It is the most common hormone therapy drug given for breast cancer.

Tamoxifen very slightly increases the risk for uterine cancer, blood clots and stroke. This is because in the uterus, blood and bones, tamoxifen acts like a weak form of estrogen (even as it stops estrogen from attaching to hormone receptor–positive breast cancer cells). Your healthcare team will talk to you about these risks when they offer tamoxifen to you. Most of the time, the benefits of taking tamoxifen outweigh the risks.

Fulvestrant is another type of anti-estrogen drug called a selective estrogen receptor degrader (SERD). It attaches to the estrogen receptors in breast cancer cells and causes the receptors to shrink and break down, or degrade.

Fulvestrant is given to people with hormone receptor–positive metastatic breast cancer that has stopped responding to tamoxifen. It can be used in both premenopausal and post-menopausal people. With premenopausal people, a gonadotropin-releasing hormone (GnRH) agonist is used with fulvestrant.

Fulvestrant may be given with the targeted therapy drug capivasertib (Truqap) for locally advanced or metastatic breast cancer that is hormone-receptor positive and HER2 negative.

Fulvestrant is given as an injection into the buttocks once a month.

After menopause, the ovaries no longer make estrogen, but it is still made by the fat tissues, adrenal glands and other areas of the body. Aromatase is an enzyme that the body uses to make estrogen in areas of the body other than the ovaries (such as fat tissues and the adrenal glands). 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 hormone receptor–positive breast cancer cells to use.

Aromatase inhibitors are given as pills. The most common aromatase inhibitors offered to treat breast cancer are:

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

Hormone therapy with aromatase inhibitors can cause bone density loss called osteoporosis. Osteoporosis can make your bones fragile and break easily. Your healthcare team may offer you drugs that help prevent, stop or slow osteoporosis while you are taking aromatase inhibitors. Find out more about osteoporosis.

Aromatase inhibitors can also cause problems with the tendons (inflammation and rupture), high cholesterol levels and sleep problems.

The pituitary gland releases luteinizing hormone and follicle stimulating hormone (FSH). These hormones tell the ovaries to make estrogen or the testicles to make hormones that can be turned into estrogen. Gonadotropin-releasing hormone (GnRH) agonists are drugs that temporarily stop the pituitary gland from releasing these hormones, which reduces the amount of estrogen that the body makes. This can help stop hormone receptor–positive breast cancer cells from growing.

The most common GnRH agonists used for breast cancer are:

• goserelin (Zoladex) – injected as a small pellet under the skin
• leuprolide (Lupron) – injected into the buttocks

Another way to slow or stop the body from making estrogen is surgery to remove the ovaries (called an oophorectomy) or the testicles (called an orchiectomy).

Hormone therapy is offered to most people with hormone receptor–positive breast cancer who have had surgery or are going to have surgery (called adjuvant hormone therapy). If you have to have chemotherapy for breast cancer, hormone therapy will be started after you have finished your chemotherapy treatments. Your healthcare team may also give you hormone therapy before surgery so you can have breast-conserving surgery.

Both premenopausal and post-menopausal people will have either tamoxifen or an aromatase inhibitor or both.

• Premenopausal people taking an aromatase inhibitor are also given a GnRH agonist at the same time.
• Premenopausal people at higher risk of breast cancer recurrence may be given tamoxifen with a GnRH agonist.

Adjuvant hormone therapy is given for a total of 5 to 10 years. You may be given:

• an aromatase inhibitor for 5 years
• tamoxifen for 2 to 3 years followed by an aromatase inhibitor for 3 to 4 years
• an aromatase inhibitor for 2 to 3 years followed by tamoxifen for 3 to 7 years
• tamoxifen for 5 to 10 years

Side effects of hormone therapy will depend mainly on the type of hormone therapy, the dose of a drug or combination of drugs and your overall health. Tell your healthcare team if you have these side effects or others that you think are from hormone therapy. The sooner you tell them of any problems, the sooner they can suggest ways to help you deal with them.

These are common side effects of hormone therapy for breast cancer:

• hot flashes, sweating and other symptoms of treatment-induced menopause
• sexual problems for people with female sex organs
• sexual problems for people with male sex organs
• weight gain
• constipation
• diarrhea
• nausea
• hair thinning
• fatigue
• fertility problems
• abnormal vaginal discharge
• increased bone or tumour pain
• depression
• headache
• body aches and pain, including back pain
• taste changes
• loss of appetite

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

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