FDA Highlights: Prophylactic anastrozole reduces breast cancer development by 53 percent among high risk women

by Bruce Sylvester – Prophylactic use of the breast cancer drug anastrozole for five years reduced by 53% the development of breast cancer in post-menopausal women at high risk for the disease, researchers  reported in the Lancet on Dec.12, 2013.

In the IBIS-II Prevention study, the investigators enrolled 3,864 postmenopausal women at high risk of breast cancer. “High risk” was defined having two or more blood relatives with breast cancer, having a mother or sister who developed breast cancer before the age of 50, and/or having a mother or sister who had breast cancer in both breasts.

The researchers randomized 1,920 subjects to anastrozole for five years and 1,944 to a placebo.

After a median monitoring up of just over five years, the investigators found  that anastrozole-treated subjects were 53 percent less likely to have developed breast cancer than placebo-treated subjects. Also, they found few side effects, mostly small increases in muscle aches and pains and in hot flashes.

Professor Jack Cuzick, lead researcher of the IBIS II trial, and head of Queen Mary University of London’s Centre for Cancer Prevention, said, “This research is an exciting development in breast cancer prevention. 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. This class of drugs is more effective than previous drugs such as tamoxifen and crucially, it has fewer side effects.”

Cuzick added, “We are planning to continue following the IBIS-II Prevention 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.”

Kate Law, director of clinical research at Cancer Research UK, said: “This landmark study shows that anastrozole could be valuable in helping to prevent breast cancer in women at higher than average risk of disease. We now need accurate tests that will predict which women will most benefit from anastrozole and those who will have the fewest side-effects.”