Hormone Therapy for Breast Cancer

Hormones are chemical messengers that travel through your body, telling it what to do. The hormones estrogen and progesterone are important for women. They impact female development, menstrual cycles, and pregnancy. But in some women, they can also increase the risk of breast cancer.

Hormone therapy for breast cancer, also called endocrine therapy, prevents cancer cells from growing by either blocking or removing the hormones.

In some cases, women may have surgery to stop making these hormones. If you’re still having periods, your doctor may suggest removing your ovaries.

When Is Hormone Therapy Used?

Not all breast cancers are fueled by hormones, or "hormone-sensitive." Those that aren’t won’t respond to hormone therapy. If you’re diagnosed with breast cancer, your health team will test your tumor to see if it’s sensitive to either estrogen or progesterone. If it’s sensitive to either or both, your doctor will prescribe you hormone-blocking treatment.

If you’ve already been treated for breast cancer, you might use hormone therapy to help keep it from coming back. It also helps lower the risk of new cancers in the other breast.

Also, if you don't have the disease but have a family history of it, or genes that raise your risk, your doctor may recommend hormone therapy to lower your chances of getting it.

What Are Common Hormone Drugs Used for Breast Cancer?

Tamoxifen blocks the activity of estrogen and is okay for women to use both before and after menopause. Men with hormone-sensitive breast cancer can take it, too.

For women with advanced cancer that’s hormone-sensitive, it’s standard treatment. If you have early stage breast cancer, or cancer that’s advanced to other areas of the breast, you may take it after surgery.

It’s also one of the drugs women at high risk of cancer may take it to lower their chances of getting cancer. The other drug approved to help lower the risk israloxifene(Evista.)

Aromatase Inhibitors

Women past menopause may get prescribed one of these drugs. After menopause, your main source of estrogen comes through a process called aromatization, in which hormones called androgens are changed into estrogen. Aromatase inhibitors fight tumor growth by stopping aromatization from happening. These drugs include anastrozole(Arimidex), exemestane(Aromasin),andletrozole(Femara).


Anastrozole is often used first for postmenopausal women with advanced hormone-positive breast cancer. It's also an add-on treatment for these women with the early form of the disease.

Exemestane is used by some postmenopausal women. If you start taking it, you’ll need to stop taking tamoxifen.

Letrozole. If you’re past menopause, and your hormone-sensitive breast cancer is advanced, your doctor may give you this drug for both initial and follow-up treatment. It’s also used as add-on therapy for early-stage breast cancer.

Palbociclib (Ibrance) is a chemotherapy drug that’s used along with letrozole. It helps slow the growth of cancer cells. A low white blood cell count is the most common side effect. You should have your blood count checked before and during treatment.

Ribociclib (Kisqali) is used in combination with an aromatase inhibitor as initial hormone therapy in women who have gone through menopause who have hormone receptor positive, HER2 negative advanced breast cancer.

If you haven’t responded well to other treatments, your doctor may suggest you take fulvestrant(Faslodex) or toremifene(Fareston).

What Are the Side Effects?

Tamoxifen can cause side effects that are similar to common menopause symptoms. You may have:

Not all women who take tamoxifen have these symptoms.

Men who take it may have headaches, nausea and vomiting, skin rash, impotence, or lesssexual interest.

There’s evidence that tamoxifen can increase the risk of cancer of the uterus. If you take it, you should have a pelvic exam every year to get checked for signs of cancer. And tell your doctor right away about any vaginal bleeding other than menstrual bleeding.

Tamoxifen has been linked to a higher risk of blood clots, especially in women who are also getting chemotherapy. It can also interfere with other drugs you may be taking.

Raloxifene has similar side effects to tamoxifen, but they're generally milder.


One serious side effect of aromatase inhibitors is bone thinning (osteoporosis). That can lead to fractures. You’ll need to have your bone density checked while taking these drugs.

With letrozole, the most common side effects are:

Some women may notice some hair thinning, but this is usually mild and goes back to normal at the end of treatment.

For anastrozole, common side effects include:

  • Hot flashes
  • Nausea
  • Less energy, and weakness
  • Back pain
  • Bone pain
  • Joint pain and stiffness
  • Coughing
  • Flu-like symptoms,
  • Swelling of the arms and legs
WebMD Medical Reference Reviewed by Laura J. Martin, MD on April 23, 2017



National Cancer Institute.

MedlinePlus: "Anastozole," "Letrozole."

UpToDate: "Anastrozole: Patient Drug information."

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