Anastrozole Cuts Postmenopausal Breast Cancer Incidence in High-Risk Women

Women at high risk of developing postmenopausal breast cancer may significantly reduce their chances of developing the disease by taking the aromatase inhibitor anastrozole

medwireNews: Anastrozole halves the 5-year rate of breast cancer in women at high risk of postmenopausal disease, indicates research reported simultaneously this week in The Lancet and at the 55th San Antonio Breast Cancer Symposium held in Texas, USA.

“This finding, along with the fact that most of the side-effects associated with oestrogen deprivation were not attributable to treatment, provides support for the use of anastrozole in postmenopausal women at high risk of breast cancer,” recommend lead author Jack Cuzick, from Queen Mary University of London, UK, and co-workers.

The IBIS-II trial shows that the 1920 women who were randomly assigned to receive anastrozole 1 mg/day were 53% less likely to develop breast cancer after a median 5 years of treatment and follow-up than were the 1944 women given placebo.

In all, 40 (2%) of the anastrozole-treated patients developed breast cancer during the study, compared with 85 (4%) controls, while the predicted cumulative 7-year incidence of breast cancer was 2.8% and 5.6%, respectively.

Therefore, 36 patients would need to be treated with anastrozole to prevent one case of breast cancer over 7 years of follow-up, the researchers explain.

"We are planning to continue following the IBIS-II Prevention participants for at least 10 years, and hopefully much longer," said Jack Cuzick in a press release.

"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."

All participants were considered to have a high risk of postmenopausal breast cancer, with 49% included on the basis of having two or more relatives diagnosed with breast or ovarian cancer, and 34% because of a mother or sister with a breast cancer diagnosis by the age of 50 years. The remainder had undergone recent treatment for oestrogen-Receptor-positive ductal carcinoma in situ (8%) or had been diagnosed with benign breast disease (9%).

Over 5 years, 68% of anastrozole-treated patients and 72% of controls adhered to treatment, with adverse events leading to 20% and 15% of patients discontinuing their drugs, respectively.

Women using anastrozole were significantly more likely than controls to report musculoskeletal adverse events (64 vs 58%), vasomotor symptoms (57 vs 49%) and dry eyes (4 vs 2%). There was also a significantly increased risk for hypertension (5 vs 3%); however, there was no significant difference seen in the rate of adverse vascular events.

Reference

Cuzick J, Sestak I, Forbes J, et al. Anastrozole for prevention of breast cancer in high-risk postmenopausal women (IBIS-II): an international, double-blind, randomised placebo-controlled trial. Lancet; Advance online publication December 13, 2013. doi:10.1016/S0140-6736(13)62292-8

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