Bone Mineral Density Changes After Anastrozole in Postmenopausal Women

The following article is part of conference coverage from the 2018 American Society for Bone and Mineral Research in Montreal, Canada. Endocrinology Advisor’s staff will be reporting breaking news associated with research conducted by leading experts on bone health. Check back for the latest news from ASBMR 2018 .

In postmenopausal women who took anastrozole, bone mineral density (BMD) showed significant improvement at the lumbar spine, according to a study presented at the American Society for Bone and Mineral Research 2018 Annual Meeting, held September 28-October 1, 2018, in Montreal, Quebec, Canada.

Previous research has found that anastrozole may prevent breast cancer in postmenopausal women; however, it is associated with accelerated BMD loss. The aim of this study was to assess changes in BMD, using dual-energy X-ray absorptiometry, 2 years after treatment cessation in women who participated in the IBIS-II breast cancer prevention trial.

In the IBIS-II trial, 3864 postmenopausal women were randomly assigned to anastrozole 1 mg/day or placebo for 5 years. A BMD substudy was conducted that included 1410 of the participants. Results were stratified into 3 strata according to their baseline T-score at spine or femoral neck (stratum I [n=760]: T-score > −1.0 and observed; stratum II [n=500]: −1.0 < T-score > −2.5 and randomly assigned to weekly risedronate or placebo; stratum III [n=150]: −2.5 < T-score > −4.0 and/or 2 fragility fractures and all receiving risedronate). 

The objective of this analysis was to investigate whether there was a change in dual-energy X-ray absorptiometry BMD at the spine and hip 2 years after stopping either anastrozole or placebo.

Data for 5- and 7-year BMD were available for 529 of the women who did not receive risedronate. There was an increase in BMD at the spine in stratum I after the cessation of anastrozole (n=205; 1.29%; 95% CI, 0.78%-1.79%), which was larger than in those receiving placebo (n=206; 0.2%; 95% CI, −0.23% to 0.62%; P =.001). BMD at the hip remained unchanged after cessation of anastrozole between 5 and 7 years, but decreased in those receiving placebo (anastrozole, −0.07% [95% CI, −0.51% to 0.37%] vs placebo, −1.31% [95% CI, −1.67% to 0.94%]; P <.0001).

Women with osteopenia (stratum II) showed similar results. Women receiving anastrozole (n=53) had significantly larger BMD increases at the spine after treatment cessation compared with women in the placebo group (n=64; anastrozole, 2.81% [95% CI, 1.40%-4.23%] vs placebo, 0.57% [95% CI, −0.36% to 1.50%]; P =.007). In women taking placebo, loss of BMD at the hip continued, but slightly increased after cessation of anastrozole (anastrozole, 0.47% [95% CI, −0.42% to 1.36%] vs placebo, −1.33% [95% CI, −2.12% to 0.54%; P =.003).

These were the first results from a breast cancer prevention setting that reported BMD changes after stopping anastrozole. There were more BMD improvements at the lumbar spine in the women originally assigned to anastrozole rather than placebo. “Our results show that negative effects of [anastrozole] on BMD in the preventive setting are partially reversible.”

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Reference

Sestak I, Cuzick J, Blake G, Patel R, Coleman R, Eastell R. Off-treatment bone mineral density changes in postmenopausal women after 5 years of anastrozole. Presented at: 2018 American Society for Bone and Mineral Research Annual Meeting; September 28-October 1, 2018; Montreal, Canada. Abstract 1142.