Arimidex® (anastrozole) reduced the risk of breast cancer by 53 percent in high-risk postmenopausal women, according to the results of a study presented at the 2013 San Antonio Breast Cancer Symposium and published simultaneously online in The Lancet.
Arimidex is a drug known as an aromatase inhibitor. Aromatase inhibitors block the production of estrogen in postmenopausal women. These drugs are commonly used in the treatment of hormone receptor-positive breast cancer, but may also have a role in breast cancer prevention—particularly in women at high risk of the disease.
The International Breast cancer Intervention Study II (IBIS-II) included 3,864 postmenopausal women at high risk of breast cancer. (High risk was defined by family history or prior diagnosis of ductal carcinoma in situ, lobular carcinoma in situ, or atypical ductal hyperplasia.) The women were randomly assigned to take 1 mg of Arimidex or placebo daily for five years. The women underwent breast exam and mammogram at baseline and every two years thereafter during the study.
After a median follow-up of five years, 40 women in the Arimidex group (2%) and 85 women in the placebo group (4%) had developed breast cancer. The predicted cumulative incidence of all breast cancers after seven years was 5.6 percent in the placebo group and 2.8 percent in the Arimidex group. The number needed to treat was 36 to prevent one breast cancer in seven years of follow-up. Side effects associated with estrogen deprivation, were only slightly more frequent in the Arimidex group than in the placebo group.
The researchers concluded that Arimidex effectively reduces the incidence of breast cancer in high-risk postmenopausal women. In fact, they found that the primary prevention effect was larger than that reported for another aromatase inhibitor, Armosain® (exemestane) and two other drugs known as selective estrogen receptor modulators (SERMs), tamoxifen and Evista® (raloxifene).
As a result of these findings, it’s likely that Arimidex will be added to the breast cancer prevention guidelines, as Aromasin was earlier in 2013.
Cuzick J, Sestak I, Forbes JF, et al. Anastrozole for prevention of breast cancer in high-risk postmenopausal women (IBIS-II): an international, double-blind, randomised placebo-controlled trial. The Lancet. Published early online December 12, 2013. doi:10.1016/S0140-6736(13)62292-8