Cyclic endogenous estrogen and progesterone vary by mammographic density phenotypes in premenopausal women

Estrogen and progesterone are key factors in the development of breast cancer, but it remains unclear whether these hormones are associated with mammographic density phenotypes in premenopausal women. We measured percent mammographic density, nondense area, and absolute mammographic density using computer-assisted breast density readings (Madena) from digitized mammograms taken on a scheduled day of the menstrual cycle (day 7-12) among 202 healthy, premenopausal women (Energy Balance and Breast cancer Aspects Study-I). Daily salivary concentrations of 17-estradiol and progesterone throughout an entire menstrual cycle and fasting morning serum concentrations of hormones on 3 specific days of the menstrual cycle were assessed. Salivary and serum 17-estradiol and progesterone were positively associated with percent mammographic density, we observed by 1SD increase in overall salivary estradiol (-value equal to 2.07, P=0.044), luteal salivary progesterone (-value equal to 2.40, P=0.020). Women with above-median percent mammographic density had a 20% higher mean salivary 17-estradiol level throughout the menstrual cycle. The odds ratio for having above-median percent mammographic density (>28.5%) per 1SD increase in overall salivary 17-estradiol was 1.66 (95% confidence interval 1.13-2.45). Women in the top tertile of the overall average daily 17-estradiol concentrations had an odds ratio of 2.54 (confidence interval 1.05-6.16) of above-median percent mammographic density compared with women in the bottom tertile. Our finding of a relationship between estrogen, progesterone, and percent mammographic density and not with other mammographic density phenotypes in premenopausal women is biologically plausible, but needs to be replicated in larger studies.