Aromatase inhibitor decreases breast cancer rate in high-risk women

MONDAY, January 13, 2020 (The Lancet) -- The aromatase inhibitor anastrozole significantly decreased long-term rates of breast cancer development in high-risk women, according to a study published in the January 11th issue of The Lancet.

Jack Cuzick, of the Wolfson Institute of Preventive Medicine at Queen Mary University in London, and colleagues measured breast cancer incidence in 3,864 high-risk women randomly assigned to 5 years of anastrozole treatment versus placebo. The current study, a continuation of The International Breast Cancer Intervention Study II (IBIS-II), followed these women from 2003 to 2012, making yearly measurements of breast cancer incidence, death, major adverse events, and the development of other cancers.

The authors measured a 49% reduction in breast cancer in the anastrozole cohort after a median follow-up of 131 months (hazard ratio [HR] 0.51, 95% CI 0.39–0.66, p<0.0001). While the incidence reduction was particularly pronounced in the first five years following treatment at 61% (0.39, 0.27–0.58, p<0.0001), the reduction in rate remains significant at 37% in subsequent years (0.64, 0.45–0.91, p=0.014). In addition, the authors reported no new late-onset adverse effects of anastrozole treatment.

“Overall, our data substantially strengthen the findings from our initial report after 5 years of follow-up,” report the authors. “The benefits of anastrozole, in terms of the reduction in risk of breast cancer in high-risk postmenopausal women, extend beyond the 5-year treatment period.”

Cuzick J, Sestak I, Forbes JF, et al. Use of anastrozole for breast cancer prevention (IBIS-II): long-term results of a randomised controlled trial. Lancet. 2019;395:117–122 doi: 10.1016/S0140-6736(19)32955-1.