The effect of baseline estradiol levels on the efficacy of anastrozole was studied

Researchers evaluated the effect of serum estradiol and testosterone concentrations on the efficacy of the aromatase inhibitor anastrozole in preventing breast cancer in high-risk postmenopausal women. The researchers suggested that regular blood hormone concentrations in such patients could help guide clinical decision-making.

Researchers from the University of London and the Universities of Manchester and Newcastle evaluated the effect of baseline serum estradiol concentration on the efficacy of anastrozole prescribed for the prevention of breast cancer in high-risk postmenopausal women. The results of the study are published in The Lancet: Oncology.

During a mean follow-up period of 11 years, breast cancer was diagnosed in 4.4% of participants in the anastrozole group and 8.5% of those taking placebo. In the placebo group, the researchers found a trend toward an increased risk of breast cancer with an increase in the ratio of estradiol to sex hormone-binding globulin (hsGH). The relationship was less pronounced for the testosterone/HSPG ratio in the placebo group. No such relationship was found in the anastrozole group.

Reduced risk of breast cancer development on the background of anastrozole administration was found in women with a higher baseline ratio of estradiol and hsCRP. Among participants whose ratio was within the second, third, and fourth quartiles, the risk of neoplasms decreased by 45%, 46%, and 44%, respectively. However, among participants with an estradiol/HSGH ratio within the first quartile, the risk reduction with anastrozole has not been proven.

They analyzed data from 3864 women aged 40-70 years with a high risk of developing breast cancer, who were observed in 153 specialized centers in 18 countries. Participants were equally divided into two groups: anastrozole orally at a dose of 1 mg/day or placebo daily for five years. They evaluated the effect of baseline estradiol to sex hormone-binding globulin ratio and baseline testosterone to hsCRP ratio on the incidence of all types of breast cancer, including ductal carcinoma in situ. Additionally, the authors evaluated the relative benefit of anastrozole versus placebo according to four quartiles of the estradiol/HCG ratio. The first quartile included participants with an estradiol/HSGH ratio below 0.176.

The authors suggest that serum hormone levels should be measured before deciding whether to prescribe anastrozole to reduce the risk of breast cancer.