Exemestane Cuts Risk of Breast Cancer in High-Risk, Postmenopausal Women

Issue 20, 2012

The drug reduced incidence by 65% and joins tamoxifen, raloxifene as chemoprevention agents

Woman taking tablet medication.

A major trial tracked nearly 4,600 women for approximately 3 years and found that the drug exemestane - already known to reduce breast cancer recurrence - may also prevent breast cancer in postmenopausal women at high risk for the disease.

Exemestane (brand name Aromasin®) comes from a class of estrogen-suppressing medications known as aromatase inhibitors (estrogen is a known 'fuel' for certain breast tumors).

As reported recently in the New England Journal of Medicine, the drug lowered users' odds for invasive breast cancer by about two-thirds. Even better, exemestane did so without some of the side effects common to two drugs from a separate class of chemopreventive agents, tamoxifen and raloxifene.

"Women and practitioners now have three options for breast cancer chemoprevention: tamoxifen, raloxifene and exemestane – agents of proven efficacy that are among the best-studied drugs in the world," Drs. Nancy Davidson and Thomas Kensler of the University of Pittsburgh wrote in an editorial accompanying the study.

For the past decade, tamoxifen and raloxifene have been mainstays of breast cancer chemoprevention for women at high risk for the disease. However, these "selective estrogen-receptor modulators" (SERMs) also raise users' risk for endometrial cancer and clot-related cardiovascular events. So, although they've been proven to reduce a woman's odds for breast cancer, Drs Davidson and Kensler note that "adoption of these targeted therapies for prevention is vanishingly rare." Enter exemestane, which had already proven its mettle in clinical trials as a means of preventing the recurrence of breast cancer in women who underwent surgery for the disease.

The new study, led by Dr. Paul Goss of the Massachusetts General Hospital Cancer Center, Boston, sought to determine whether the drug might reduce the incidence of this malignancy in postmenopausal women deemed to be at higher risk. These risk factors included being over 60 years of age, rating unfavorably on a standard breast cancer "risk score," and/or having a prior history of pre-cancerous abnormalities in breast tissue.

The study (funded in part by Aromasin's® maker, Pfizer) randomized 4,560 such women to receive either exemestane or a placebo daily, with follow-up lasting about 3 years.

The result: 11 women in the exemestane group developed invasive breast cancer compared to 32 of the women taking a placebo, a 65 percent reduction in risk. According to the authors, that equals the prevention of one case of breast cancer for every 94 women taking the drug over 3 years.

Exemestane users did not experience any increase in risk for endometrial cancer or cardiovascular trouble over the course of the study (as has been noted with tamoxifen or raloxifene). However, they did experience more hot flashes and arthritic joint stiffness compared to women on placebo. Nevertheless, women on exemestane did not rate their overall quality of life as being any worse than did the women on placebo, and the authors believe the drug has "an excellent safety profile."

Dr. Goss and colleagues acknowledge that 3 years is relatively short follow-up, but they are optimistic that exemestane’s benefits in preventing breast cancer will persist.

As for Drs. Davidson and Kensler, they note that as genomic testing evolves over time, physicians may get better at determining which women will benefit the most from exemestane and other chemopreventive medications.

Overall, they wrote, the findings "support the use of exemestane as an option for risk reduction in postmenopausal women at high risk for breast cancer."