Aromatase Inhibitors

Updated 
August 31, 2015
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The aromatase inhibitors, or AIs, are a class of medicines that reduce the risk of breast cancer returning in postmenopausalinfo-icon women with hormone receptorinfo-icon-positive, early-stage breast cancerinfo-icon. They are also a standard treatment for metastaticinfo-icon disease.

There are three FDAinfo-icon approved aromatase inhibitors for all stages of breast cancer:

How Aromatase Inhibitors Work

After menopauseinfo-icon, your body stops making estradiolinfo-icon, the main estrogeninfo-icon produced by the ovaries. But your body still makes estrone, an estrogen created by converting a male sex hormoneinfo-icon found in the adrenal glands, fat cells and muscle. The enzyme aromatase converts that hormone into estrogen. Fat cells and other body parts also do so as well.

Aromatase inhibitors interfere with the enzyme aromatase to decrease the female hormones in your body. It then can reduce the risk of breast cancer returning, or control the growth of metastaticinfo-icon disease.

Anastrozoleinfo-icon, exemestaneinfo-icon and letrozoleinfo-icon work similarly to one another. Talk with your doctors about why they recommend one AI over another.

Who Gets Aromatase Inhibitors

All three aromatase inhibitors are given to postmenopausalinfo-icon women with hormone receptorinfo-icon-positive breast cancer. Any of the AIs may be the first or primary hormonal therapyinfo-icon your doctor prescribes if you have early-stageinfo-icon disease because aromatase inhibitors are the standard hormonal therapy for postmenopausal women.

If you have metastaticinfo-icon breast cancer, you may receive any of the three aromatase inhibitors as a first treatment after your stage IV diagnosisinfo-icon. Your doctor may also recommend:

How Aromatase Inhibitors Are Given

The AIs are all given as daily pills. In early-stageinfo-icon disease they are usually given after surgeryinfo-icon, radiationinfo-icon or chemotherapyinfo-icon. They are FDAinfo-icon approved to be given for 5 years after surgery, or for 5 years after up to 5 years of tamoxifeninfo-icon for a total of 10 years of hormonal therapyinfo-icon.

In 2014, findings from a clinical trialinfo-icon suggested premenopausalinfo-icon women who use LHRH agonists to temporarily stop the function of their ovaries may be able to safely take exemestaneinfo-icon. Exemestane is not yet FDA approved for this purpose but your doctor may discuss this option with you if you have not yet gone through menopauseinfo-icon.

In metastaticinfo-icon breast cancer, any of the AIs may be the first treatment given if you are postmenopausalinfo-icon and have hormoneinfo-icon-positive disease. They may be paired with other treatments or given alone. You may take one medicineinfo-icon for as long as it works at controlling the cancer. Your doctor may then recommend you try a different medicine.

Side Effects and Things to Remember

With hormonal therapies, we don’t know why some women experience difficult side effects when others, taking the same medicineinfo-icon, have mild or no problems. Always talk with your providers about what you’re feeling.

If side effects from a certain aromatase inhibitorinfo-icon become too difficult or interfere with your ability to function, your doctor might suggest another AI for you. Even though the AIs work in similar ways, a different aromatase inhibitor may not cause the same side effects for you. It’s likely you can switch to another medicine and see if that helps. Consider a second opinion if your doctor won’t discuss your concerns with you. Never stop treatment on your own without speaking with your providers first.

Possible side effects of the AIs are:

  • stiffness, and joint and bone pain
  • bone thinning and fractures
  • high blood pressure
  • higher cholesterol
  • fatigueinfo-icon and insomniainfo-icon
  • nauseainfo-icon and vomiting
  • hot flashes
  • weakness
  • headache
  • vaginal dryness
  • loss of appetite
  • weight gain
  • mood changes
  • constipation or diarrheainfo-icon
  • dry skin
  • hair thinning

You can also go to our section on Side Effects for more information.

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Article August 31, 2015