Association of high mammographic density with hormone replacement therapy and other risk factors

Mammographic density adversely affects diagnostic accuracy and is a relatively strong risk factor for breast cancer. Mammographic density itself may be affected by hormone replacement therapy (HRT) and other risk factors. If high mammographic density is causally related to breast cancer, rather than being only a correlate of risk, then modification of the factors which affect breast density could be an important intervention strategy to reduce breast cancer risk.; The objective of this cohort study was to determine the association between high mammographic density (more than 75% density) and hormone replacement therapy and other risk factors. Subjects were 14,026 women aged 50 years and older enrolled in the Ontario Breast Screening Program (OBSP) in the Southeast region from 1997 to 2000 with mammographic density information. Data from the initial screening report, such as hormone replacement therapy use and covariates, were obtained from the OBSP.; Results showed very strong dependence on age of both the exposure (HRT) and outcome variable (high mammographic density). Results adjusted for screening age showed strong association between high mammographic density and HRT, but generally not on duration or timing of HRT use. Results for other risk factors indicated that menopausal status, number of children, history of gynaecological surgery, and benign breast disease were the factors statistically significantly associated with high mammographic density. Factors that were not associated with high mammographic density were started using HRT in current users, duration of past HRT use, and breast symptoms.