Arimidex Extends Benefit of Breast Cancer Recurrence Prevention in Postmenopausal Women

Women treated with Arimidex for five years were 50% less likely to have developed breast cancer recurrence compared with women given placebo at nearly 11 years follow-up after stopping treatment.
BY Tom Castles and Katie Kosko
PUBLISHED December 12, 2019
Arimidex (anastrozole) is an effective way to reduce the risk of breast cancer recurrence in postmenopausal women who are at increased risk for the disease, according to study findings presented during the 2019 San Antonio Breast Cancer Symposium.

The latest data from the International Breast Cancer Intervention Study II were also simultaneously published in The Lancet.

Researchers found that the effects of the aromatase inhibitor persisted for nearly 11 years.

Nearly 4,000 postmenopausal women, ranging in ages 40 to 70 years old and who were considered at high risk of developing breast cancer, were enrolled in the trial from 2003 to 2012. High risk considerations included women who had two or more blood relatives with breast cancer, had a mother or sister who developed breast cancer before age 50 or had a mother or sister who had breast cancer in both breasts.

Patients were chosen at random to either receive Arimidex (1,920 patients) or placebo (1,944 patients) for five years. Treatment adherence was similar among both groups, with 74.6% of patients on Arimidex following the treatment regimen for the full five years and 77% following through in the placebo group.

After a median follow-up of 10.9 years, women assigned to Arimidex were 50% less likely to have developed breast cancer compared with women assigned to placebo, the researchers reported.

“Another way to consider the data is that it translates into an estimated 29 women needing to be treated with anastrozole for five years to prevent one breast cancer during treatment and in the next five years,” Dr. Jack Cuzick, cochairman of the International Breast Cancer Intervention Studies, said in a press release. “This is far fewer women than the estimated 49 women that need to be treated with tamoxifen for five years to prevent one breast cancer in the same time period.”

Invasive oestrogen receptor positive breast cancer was reduced by 54% with Arimidex. In addition, there was a reduction in ductal carcinoma in situ, with a very large reduction in those with ER-positive disease. No significant benefit was seen for women with estrogen receptor–negative breast cancer.

“It is exciting to see that anastrozole has a continued impact on breast cancer incidence even after stopping treatment, as this strengthens the case for its use as a breast cancer prevention therapy,” Cuzick said.

Moreover, the drug was well tolerated by patients, who experienced side effects such as muscle aches and pains and hot flashes, which were probably not attributable to the drug, but to aging, Cuzick said during a press conference.

At the time of analysis, 129 deaths had been reported. However, five deaths were from breast cancer — two assigned Arimidex and three assigned placebo.

“Our new results strongly suggest that anastrozole should be the preferred therapy for breast cancer prevention in postmenopausal women at increased risk for the disease, with tamoxifen used for women who experience severe side effects from anastrozole,” Cuzick said.
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