Does HRT raise risk of breast cancer in thin or obese women?

A new registry-based study sheds light on patient factors that may influence risk of breast cancer associated with use of postmenopausal hormone replacement therapy (HRT)-including race, weight, and breast density. Findings from the report, published in The Journal of the National Cancer Institute, suggest the greatest association between HRT use and breast cancer in women with low/normal body mass index (BMI) and extremely dense breasts.

Data for the study, by researchers from the University of Chicago, were from the Breast Cancer Surveillance Consortium, a longitudinal registry of mammography screening in the United States. The analysis included 164,824 screening mammograms from 9300 breast cancer cases in postmenopausal women aged 45 and older. Missing data on HRT use and other covariables were accommodated by using multiple imputation methods.

The researchers used logistic regression to estimate the odds ratio (OR) for breast cancer associated with HRT use and stratify it by race/ethnicity, age, BMI, and breast density. Two-way interaction terms between HRT use and each key covariable of interest were part of the computations. P values for possible interactions were computed from Wald z statistics and all statistical tests were two-sided.

Use of HRT was associated with >20% increased risk of breast cancer in white (OR=1.21; 95% CI = 1.14-1.28), Asian (OR=1.58; 95% CI = 1.18-2.11), and Hispanic women (OR=1.35; 95% CI=1.09-1.67) but not black women (OR=0.91; 95% CI = 0.72-1.14). The highest risk of breast cancer with HRT use was seen in women with low/normal BMI and extremely dense breasts (OR=1.48; 95% CI = 1.21=1.83) compared with nonusers. No excess risk of breast cancer was associated with HRT use in overweight/obese women with less-dense breasts (adjusted ORs=0.96-1.03). Risk stratification, the researchers concluded, could be of help to clinicians in counseling women about use of HRT for menopausal symptoms.

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