Abstract P6-09-02: Risk of Breast Cancer Associated with Hormone Replacement Therapy Use Differs by Age, Race, and Breast Density

Background: Observational studies and randomized trials have demonstrated an association between hormone replacement therapy (HRT) use and increased risk for breast cancer. However, this risk may vary by age and other factors, including breast density and race/ethnicity. Using data from the Breast Cancer Surveillance Consortium (BCSC), we investigate whether self-reported HRT use in the peri-menopausal and immediate post-menopausal age groups is associated with breast cancer, and also whether risk associated with HRT use differs by breast density and race. Subjects and Methods: The BCSC is a longitudinal registry of mammography screening in seven U.S. centers. In the breast cancer risk prediction model developed by Barlow et al (J Natl Cancer Inst 2006 98:1204-14), HRT use and ten other features were identified as risk factorsfor breast cancer. Data for our study consists of 1,642,824 screens and 9,300 breast cancers among the post-menopausal women aged > 44 in this cohort. Logistic regression models were used to estimate odds ratios for breast cancer associated with HRT use within race, age, and density strata, adjusting for other variables from the Barlow model. Multiple imputation methods were used to accommodate missing data for HRT (14%) and other predictors. Results: Breast cancer risk for HRT use varied by age, with no risk excess among women aged 45-49 and risk excess of 20% or greater for women aged 50-64 (Table 1). Women >64 had a smaller excess risk with HRT use. There was no significant excess risk at any age for Black women, while White women age 50-64 had > 20% excess risk for HRT use. White women with higher breast density had increased risk with HRT use, while Black women did not. Table 1: Odds ratios (95% confidence interval) for HRT use (yes/no) Conclusions: In this large cohort of mammography-screened women, HRT use did not increase breast cancer risk in the peri-menopausal period (age 45-49). Women with low breast density had smaller risk increments associated with HRT than those with high density. For Black women, increased breast cancer risk due to HRT was not apparent at any age or breast density category. Data collection for the BCSC was supported by a NCI-funded Breast Cancer Surveillance Consortium co-operative agreement (U01CA63740, U01CA86076, U01CA86082, U01CA63736, U01CA70013, U01CA69976, U01CA63731, U01CA70040). Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-09-02.