By Steven Reinberg
NEW YORK (Reuters Health) – In postmenopausal women, increased estradiol levels are associated with a high risk of developing breast cancer, suggesting that these women may benefit most from raloxifene therapy, researchers report in the Journal of the American Medical Association for January 9.
Women with high levels of estrogen have a high risk of breast cancer, whereas women with very low estrogen levels have a low risk of breast cancer that is not further reduced by drug therapy, lead author Dr. Steven R. Cummings from the University of California, San Francisco, told Reuters Health.
Dr. Cummings and colleagues studied 7705 postmenopausal women with osteoporosis, mean 66.5 years of age, who participated in the Multiple Outcomes of Raloxifene Evaluation trial. Of these women, 7290 had measurements of estradiol at baseline. All the women, none of whom had received HRT, were randomly assigned to raloxifene at 60 mg/day or 120 mg/day or to placebo.
Over 4 years, 74 cases of breast cancer were diagnosed. Women in the placebo group with estradiol levels more than 10 pmol/L had a 6.8-fold increased risk of breast cancer compared with women whose estradiol levels were undetectable (p = 0.005 for trend).
Women in the raloxifene group with estradiol levels above 10 pmol/L had a 76% lower rate of breast cancer compared with women in the placebo group with similar estradiol levels, the researchers found.
However, women with undetectable estradiol levels had a similar risk of developing breast cancer whether they received raloxifene or placebo, Dr. Cummings' team notes.
The investigators estimate that 47% of the breast cancer cases in women with estradiol levels above 10 pmol/L would have been prevented if these women had been receiving raloxifene for 4 years.
"It is worrisome to know that a woman's risk of developing breast cancer depends on her estrogen level," Dr. Cummings said. It appears that women taking estrogen replacement are increasing their risk of breast cancer, he added.
Dr. Cummings and colleagues conclude that if their findings are "confirmed by other studies, measuring estradiol to determine breast cancer risk may help identify women likely to experience the greatest reduction in breast cancer risk from treatment with raloxifene."