Aromasin Reduces Risk But Weakens Bones

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Aromatase inhibitors are hormonal therapy medicines used to treat breast cancer and help stop breast cancer from coming back (recurrence) in postmenopausal women. Doctors have been interested in using aromatase inhibitors to reduce breast cancer risk in postmenopausal women at high risk who haven't been diagnosed.

Results from the MAP.3 trial found that the aromatase inhibitor Aromasin (chemical name: exemestane) was good at lowering breast cancer risk in high-risk postmenopausal women, but weakened bones. The research was published Feb. 7, 2012 online in The Lancet Oncology.

Other hormonal therapy medicines often are prescribed to premenopausal and postmenopausal women at high risk of breast cancer to reduce risk. Doctors call this type of treatment primary prevention. Tamoxifen (brand name: Nolvadex) is used for primary prevention in both premenopausal and postmenopausal women; Evista (chemical name: raloxifene) is used for primary prevention only in postmenopausal women.

In addition to lowering breast cancer risk in women at high risk, both tamoxifen and Evista actually can strengthen bones. Tamoxifen and Evista are SERMs (selective estrogen receptor modulators). SERMs block the action of estrogen in breast and certain other cells by sitting in the cells' estrogen receptors. SERMs don't affect all estrogen receptors the same way because they're selective (as the name says). In bone cells, SERMs interact with the receptors the way estrogen does and strengthen bones. In breast cells, SERMs block the receptors' interaction with estrogen and limit cell growth.

Aromasin and other aromatase inhibitors work by stopping the body from producing estrogen, which limits the amount of estrogen available to stimulate hormone-receptor-positive breast cancer cells to grow. Aromatase inhibitors currently aren't used to reduce breast cancer risk in high-risk postmenopausal women.

The other aromatase inhibitors are:

  • Arimidex (chemical name: anastrozole)
  • Femara (chemical name: letrozole)

The side effects of tamoxifen and Evista -- primarily hot flashes and night sweats, sometimes severe -- can be very bothersome to some high-risk postmenopausal women. So a different primary prevention treatment option could be good for them. The large MAP.3 study (more than 4,500 women participated) was designed to see if Aromasin could be a useful primary prevention treatment for postmenopausal high-risk women.

Half the women in MAP.3 were followed for more than 3 years; the other half for shorter periods of time. Women who got Aromasin were 65% less likely to be diagnosed with breast cancer compared to women who got a placebo (sugar pill). During follow-up:

  • 32 out of 2,275 women who got the placebo were diagnosed with breast cancer compared to 11 out of 2,285 women who got Aromasin

The lower estrogen levels of women taking an aromatase inhibitor can lead to bone loss during treatment. The researchers looked at the bone health of 351 women in the MAP.3 study -- all had healthy bones at the study's start -- and found that bone health declined more in women who got Aromasin compared to women who got the placebo.

Bone mineral density, a common bone strength test, in the tibia (lower leg bone) dropped 7.6% in women who got Aromasin compared to only 0.7% in women who got the placebo.

If you're a postmenopausal woman with a higher-than-average risk of breast cancer, you already may be taking medicine to help keep your risk as low as it can be. If not, you might want to ask your doctor if taking a SERM -- tamoxifen or Evista -- makes sense for you. Besides lowering your breast cancer risk, these medicines can help strengthen your bones. You and your doctor may consider an aromatase inhibitor (such as Aromasin) as an alternative to a SERM, particularly if you're having unacceptable side effects on a SERM. But it's important to know that an aromatase inhibitor could weaken your bones over time. Always talk to your doctor about the benefits and risks of any treatment you're considering. Together, you can make the best choice for your unique situation.

You can learn more about tamoxifen, Evista, and Aromasin in the Breastcancer.org Hormonal Therapy section.

Editor's Note: In July 2013, the American Society of Clinical Oncology put out new guidelines on using hormonal therapy medicines to reduce breast cancer risk in high-risk undiagnosed women. Besides tamoxifen and Evista, the guidelines also recommend that doctors talk to postmenopausal high-risk women about using the aromatase inhibitor Aromasin (chemical name: exemestane) to reduce risk.

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