Anastrozole Cuts Breast Cancer Risk By 50% In Older, High-Risk Women

Issue 24 Winter/Spring 2015

Aromatase inhibitor reduces incidence of estrogen-sensitive cancer, with few side effects, study finds

Picture of elderly person taking prescription

Postmenopausal women at high risk of breast cancer may have a powerful new ally: A new study finds the drug anastrozole (Arimidex®) halves their odds of developing the disease.

The drug also seems to have fewer side effects than other preventive medicines such as tamoxifen or raloxifene, researchers found.

"The research is an exciting development in cancer prevention," said lead researcher Dr. Jack Cuzick, director of the Center for Cancer Prevention at Queen Mary University of London, in the U.K.

"We now know anastrozole should be the drug of choice when it comes to reducing the risk of breast cancer in postmenopausal women with a family history or other risk factors for the disease," he said. "This class of drugs is more effective than previous drugs such as tamoxifen and crucially, it has fewer side effects."

That's important, because drugs aimed at preventing breast cancer often have low rates of patient adherence. In the study, published earlier this year in The Lancet, approximately 70 percent of women complied with the regimen over the 5 years of the trial.

The research involved almost 4,000 women drawn from cancer centers in 18 countries. All were postmenopausal and were deemed to be at high risk for breast cancer because of factors such as: blood relatives having already developed the disease before the age of 50; having a mother or sister who developed tumors in both breasts; or having certain high-risk benign breast conditions.

Anastrozole is designed to reduce the incidence of estrogen-sensitive breast cancers. It does so by inhibiting aromatase, an enzyme crucial to the production of the hormone.

Cuzick's team found that, over 5 years, 40 of the nearly 2,000 women taking anastrozole developed breast cancer, compared to 85 of the nearly 2,000 who took a placebo – a 53 percent reduction. As expected, the benefit was limited to estrogen-sensitive breast cancers; the drug had no impact on the incidence of other breast tumor types.

Women also seemed to tolerate anastrozole relatively well. "Unpleasant side effects such as acute aches and pains have often been associated with estrogen depriving drugs," Cuzick noted. "However, the reported side effects [in the study] were only slightly higher than in the placebo arm. This means most symptoms were not drug-related."

Experts note that another aromatase inhibitor, exemestane, has also been shown to be effective in preventing breast cancer. Additionally, both tamoxifen and raloxifene, antagonists of the estrogen receptor, reduce the risk of estrogen-sensitive breast cancers.

The study was funded by Cancer Research UK, the National Health and Medical Research Council Australia, and drug makers Sanofi-Aventis and AstraZeneca.

According to experts, the goal is to now make sure that more women at high risk of breast cancer understand they have another option to help prevent the disease.

Pinpointing those women who stand to benefit most from anastrozole may be the next step, according to Kate Law, director of clinical research at Cancer Research UK. "We now need accurate tests that will predict which women will most benefit from anastrozole and those who will have the fewest side-effects," she said.

In the meantime, Cuzick said he and his colleagues will continue their research, tracking the trial participants "for at least 10 years, and hopefully much longer."

"We want to determine if anastrozole has a continued impact on cancer incidence even after stopping treatment, if it reduces deaths from breast cancer, and to ensure that there are no long-term adverse side effects," he said.