Mammographic density represents a strong and independent breast cancer risk factor, and possibly a useful surrogate endpoint for breast cancer risk. Mammographic density decreases when women undergo menopause or start tamoxifen therapy, but increases in w omen starting postmenopausal hormone therapy with combined estrogen and progestin. There is, however, substantial variation in how mammographic density changes when hormone exposure changes, but the genetic predictors of this change is unknown. Because of the role of hormones in breast cell proliferation, genetic predictors involved in hormone metabolism or action seem plausible candidates in explaining ‘endogenous’ mammographic density. Identifying these genes is important as they may provide important c lues to hormonal carcinogenesis of the breast.
We are proposing to identify genetic predictors of mammographic density in women on and in women not on hormone therapy among women in the Norwegian Breast Cancer Screening Program (NBCSP), a national mammogr aphic screening program. We will also provide pilot data as to whether genetic predictors for mammographic density explain breast cancer risk.