Hormone therapy to treat breast cancer uses drugs or treatments to lower levels or block the action of female sex hormones (estrogen and progesterone) in a woman's body. This helps slow the growth of many breast cancers.
Hormone therapy makes cancer less likely to return after breast cancer surgery. It also slows the growth of breast cancer that has spread to other parts of the body.
Hormone therapy can also be used to help prevent cancer in women at high risk for breast cancer.
It is different from hormone therapy to treat menopause symptoms.
Drug Side Effects
The side effects of hormone therapy depend on the drug. Common side effects include hot flashes, night sweats, and vaginal dryness.
Some drugs can cause less common but more serious side effects, such as:
- Tamoxifen. Blood clots, stroke, cataracts, endometrial and uterine cancers, mood swings, depression, and loss of interest in sex.
- Aromatase inhibitors. High cholesterol, heart attack, bone loss, joint pain, mood swings, and depression.
- Fulvestrant. Loss of appetite, nausea, vomiting, constipation, diarrhea, stomach pain, weakness, and pain.
Drugs That Block Estrogen
Some drugs work by blocking estrogen from causing cancer cells to grow.
Tamoxifen (Nolvadex) is a drug that prevents estrogen from telling cancer cells to grow. It has a number of benefits:
- Taking Tamoxifen for 5 years after breast cancer surgery cuts the chance of cancer coming back by half. Some studies show that taking it for 10 years may work even better.
- It reduces the risk that cancer will grow in the other breast.
- It slows the growth and shrinks cancer that has spread.
- It reduces the risk of getting cancer in women who are high risk.
Other drugs that work in a similar way are used to treat advanced cancer that has spread:
- Toremifene (Fareston)
- Fulvestrant (Faslodex)
Drugs That Lower Estrogen Levels
Some drugs, called aromatase inhibitors (AIs), stop the body from making estrogen in tissues such as fat and skin. But, these drugs do not work to make the ovaries stop making estrogen. For this reason, they are used mainly to lower estrogen levels in women who have been through menopause (postmenopausal). Their ovaries no longer make estrogen.
Premenopausal women can take AIs if they are also taking drugs that stop their ovaries from making estrogen.
Aromatase inhibitors include:
- Anastrozole (Arimidex)
- Letrozole (Femara)
- Exemestane (Aromasin)
Hormones and Breast Cancer
The hormones estrogen and progesterone make some breast cancers grow. They are called hormone-sensitive breast cancers. Most breast cancers are sensitive to hormones.
Estrogen and progesterone are produced in the ovaries and other tissues such as fat and skin. After menopause, the ovaries stop producing these hormones. But the body continues to make a small amount.
Hormone therapy only works on hormone-sensitive cancers. To see if hormone therapy may work, doctors test a sample of the tumor that has been removed during surgery to see if the cancer might be sensitive to hormones.
Hormone therapy can work in two ways:
- By blocking the estrogen from acting on cancer cells
- By lowering estrogen levels in a woman's body
Lowering Estrogen Levels From the Ovaries
This type of treatment only works in premenopausal women who have functioning ovaries. It can help some types of hormone therapy work better. It is also used to treat cancer that has spread.
There are three ways to lower estrogen levels from the ovaries:
- Surgery to remove the ovaries
- Radiation to damage the ovaries so they no longer function, which is permanent
- Drugs such as goserelin (Zoladex) and leuprolide (Lupron) that temporarily stop the ovaries from making estrogen
Any of these methods will put a woman into menopause. This causes symptoms of menopause:
- Hot flashes
- Night sweats
- Vaginal dryness
- Mood swings
- Loss of interest in sex
Weighing the Options
Deciding on hormonal therapy for breast cancer can be a complex and even difficult decision. The type of therapy you receive may depend on whether you have gone through menopause before treatment for breast cancer. It also may depend on whether you want to have children. Talking with your health care provider about your options and the benefits and risks for each treatment can help you make the best decision for you.
American Cancer Society website. Hormone therapy for breast cancer.
National Cancer Institute website. Hormone therapy for breast cancer.
Rugo HS, Rumble RB, Macrae E, et al. Endocrine therapy for hormone receptor-positive metastatic breast cancer: American Society of Clinical Oncology Guideline. J Clin Oncol. 2016;34(25):3069-3103. PMID: 27217461
Wolff AC, Domchek SM, Davidson NE, Sacchini V, McCormick B. Cancer of the breast. In: Niederhuber JE, Armitage JO, Doroshow JH, Kastan MB, Tepper JE, eds. Abeloff's Clinical Oncology. 5th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 91.