What are Aromatase Inhibitors & How Do They Work?|Types|Benefits|Side Effects

What are Aromatase Inhibitors?

Aromatase inhibitors are a class of drugs which are used for treatment of hormone receptor-positive early and metastatic breast cancer in postmenopausal women. Aromatase inhibitors are used to stop the production of estrogen in postmenopausal women. They work by blocking the enzyme aromatase which turns the hormone androgen into small quantity of estrogen in the body. This indicates that there is less estrogen in the body to simulate the growth of the hormone receptor positive breast cancer cells. Hormone receptor-positive breast cancer can be treated by hormone therapy with tamoxifen and/or an aromatase inhibitor (anastrozole, letrozole or exemestane) which is a part of the treatment.

What are Aromatase Inhibitors?

What are the Types of Aromatase Inhibitors?

Aromatase is a kind of enzyme which synthesizes estrogen. When estrogen is synthesized in the body then there are less chances of breast cancer spreading. There are three types of aromatase inhibitors:

  • Arimidex
  • Aromasin
  • Femara

When Should Aromatase Inhibitors Be Used?

People who are still undergoing their menstrual cycle need not take aromatase inhibitors. Aromatase inhibitors don’t stop the ovaries from making estrogen, hence aromatase inhibitors are recommended for woman whose menstrual cycle is stopped. When compared to tamoxifen, aromatase inhibitors are more effective for postmenopausal woman. Researchers wondered if there is any way to treat premenopausal woman who are diagnosed with hormone-receptor-positive with aromatase inhibitors. In 2015, results from SOFT (Suppression of Ovarian Function Trial) successfully published that premenopausal women who are suffering from hormone-receptor-positive breast cancer can be treated with aromatase inhibitors only if their ovarian function is suppressed. If you are still undergoing your menstrual cycle and willing to suppress your ovaries then you can take Aromasin rather than using tamoxifen for hormonal therapy treatment.

When Should You NOT Use Aromatase Inhibitors?

Aromatase inhibitors must never be used if you are pregnant, trying to get pregnant, breast feeding and if there are any chances of you getting pregnant. When you use aromatase inhibitors when you are pregnant they damage the embryos. Make sure to use an appropriate non-hormonal birth control such as, condoms, non-hormonal I.U.D. when you are consuming aromatase inhibitors. If you are suffering from receptor-positive early and metastatic breast cancer, make sure you check with your doctor for a non-hormonal birth control tablets which are suitable for you.

What are the Benefits of Aromatase Inhibitors?

A lot of research has been done to check the effectiveness and success rates of treating early stages of receptor-positive early and metastatic breast cancer in postmenopausal woman using aromatase inhibitors and tamoxifen. Check out the various benefits of aromatase inhibitors:

  • During the early stages of receptor-positive early and metastatic breast cancer, aromatase inhibitors are the best to start with. When they are used in the early stages they are the best with no serious side effects caused when compared to tamoxifen.
  • The benefits of switching from tamoxifen to aromatase inhibitors are more. This includes a total of 5 years of hormonal therapy.
  • When you use aromatase inhibitors for 5 years and later start taking tamoxifen for 5 years, then this will reduce the risk of recurrent cancer.

How Do Aromatase Inhibitors Work?

Estrogen and/or progesterone are needed for the spread or growth of Hormone receptor-positive breast cancers. Estrogens are female hormones produced in the body. Aromatase inhibitors are hormone therapy drugs which can slow or stop the production of hormone receptor-positive tumors. The estrogen level is reduced in the body by blocking aromatase. Aromatase is an enzyme which converts other hormones into estrogen. This in turn prevents the growth of the cancer cell from growing.

How are Aromatase Inhibitors Consumed?

  • Aromatase inhibitors are available in pill forms. One pill a day is sufficient or can be consumed as prescribed by the doctor.
  • A postmenopausal women suffering from hormone receptor-positive breast cancer can begin the hormonal therapy by using aromatase inhibitors.
  • Initially one can begin with tamoxifen and later they can switch to aromatase inhibitors. When you consume only aromatase inhibitors, then the chances of reducing receptor-positive breast cancer are within 7-10 years. When aromatase inhibitors and tamoxifen is combined, then receptor-positive breast cancer can be reduced within 8 years.
  • Consult your Oncologist regarding the consumption of aromatase inhibitors, as it varies from person to person based on their stages.

What are the Side Effects of Aromatase Inhibitors?

Aromatase inhibitors are the perfect hormonal therapy, which is used to cure receptor-positive breast cancer. When compared to chemotherapy, there are various side effects which are caused by using aromatase inhibitors.

  • Joint pain and muscle pain is the common side effects of aromatase inhibitors. The pain may be in the wrists, hands, feet, ankles, knees and other parts of the body. When you have joint pains while consuming aromatase inhibitors, consult with your doctor as they may prescribe anti-inflammatory medications.
  • You will suffer from loss of bone density which leads to osteoporosis and bone fractures when taking aromatase inhibitors. You will have to undergo bone strengthening therapy and regular exercise. Make sure to quit smoking and drinking to combat this side effect of aromatase inhibitors.
  • Night sweats and hot flashes are a common side effect in women who consume aromatase inhibitors. If you come across any such symptoms make sure to consult your doctor.


In a recent research, comparison was done among patients who consumed tamoxifen and aromatase inhibitors (letrozole) for 10 years versus 5 years. Women who consumed letrozole for 10 years had improved disease free survival and the risk of cancer in the opposite breast also reduced. Women who consumed tamoxifen continued to have various side effects such as high rate of osteoporosis and bone fractures.

Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:June 5, 2019

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