Hormone Therapy

Hormone therapy is a treatment option for some breast cancers. Hormones like estrogen and progesterone play a role in these cancers. Thus, endocrine therapy is another name for this kind of treatment.1

How hormone therapy works

Hormone therapy works for breast cancers that are hormone receptor-positive (HR+). HR+ breast cancers account for about 60 percent of all breast cancers. Subtypes of these cancers exist such as estrogen or progesterone receptor-positive (ER+ or PR+).1

In HR+ breast cancers, proteins or receptors on the cancer cells link to hormones in the body. The cancer cells feed on these hormones. As a result, the cancer cells increase in number, resulting in tumor growth.1,2

Hormone therapy works in diverse ways, depending on the specific therapy chosen. Most hormone therapies work to reduce the presence and function of estrogen in the body. Some keep estrogen from reaching the cancer cells and taking effect.1,2

The goals of hormone therapy may vary from person to person. One aim is to prevent breast cancer in women at risk. Hormone therapy can also be used to keep cancer from recurring when taken after breast cancer surgery. People may undergo hormone therapy to slow or stop the spread of breast cancer that has returned following treatment or has already begun to spread to areas of the body beyond the breast.1,2

Types of hormone therapy

A few types of hormone therapy exist. Most are systemic. A person takes a pill or gets an injection that releases a drug throughout the body. The drugs include anti-estrogens or aromatase inhibitors. Other drugs stop the ovaries from working, to reduce estrogen levels in the body.1-5

Surgery is a type of local hormone therapy. Surgery focuses on a certain part of the body such as the ovaries.1-3

Anti-estrogens

Anti-estrogens block estrogen receptors or proteins on the cancer cells. These drugs attach to the proteins. This prevents the cells from connecting with the estrogen that promotes growth.1,2,4

Anti-estrogens used to treat certain forms of breast cancer include:1,2,4

  • Fareston® (toremifene)
  • Faslodex® (fulvestrant)
  • Nolvadex® (tamoxifen)

Aromatase inhibitors

Aromatase inhibitors keep the body from making estrogen. They block the aromatase enzyme used to make estrogen outside the ovaries. Doctors prescribe this treatment mainly for women whose periods have stopped.1,2,5

Aromatase inhibitors used to treat certain forms of breast cancer include:1,2,5

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

Measures to stop the ovaries

Measures to stop the ovaries are another kind of hormone therapy. The ovaries produce much of the estrogen in the body. Taking out the ovaries through surgery, for example, will reduce estrogen.1-3

Some drugs can also halt the function of the ovaries. For example, Lupron Depot® (leuprolide acetate) and Zoladex® (goserelin) block certain hormones the ovaries need to make estrogen.1-3

Common side effects of hormone therapy

Side effects of certain hormone therapies can vary and range from minor to serious. Not every person responds to each treatment in the same way. One person may have only a few, small side effects. Someone else could react in a more adverse way.

Common side effects that may occur with some hormone therapies include:1,2,4,5

  • Breast tenderness
  • Fatigue
  • Hair loss
  • Headaches
  • Hot flashes
  • Joint stiffness
  • Lower sex drive
  • Mood swings
  • Nausea
  • Night sweats
  • Pain in bones, joints, and muscles
  • Vaginal discharge and dryness
  • Weight gain

Certain hormone therapies can also cause more severe side effects such as:1,2,4,5

  • Blood clots
  • Bone loss and weakness
  • Increased risk of other cancers
  • Strokes

These are not all the possible side effects of hormone therapy.

Before starting hormone therapy, tell your doctor about all your health conditions. Inform your doctor of any other drugs, supplements, or vitamins you are taking. This includes over-the-counter drugs.

Talk to your doctor about what to expect from your hormone therapy. This will help you know what to watch for once you start treatment. Share with your doctor any changes that concern you such as new or worse symptoms. They can then advise you and adjust your treatment plan as needed.

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Written by: Editorial Team | Last reviewed July 2021.