Objective: The objective of this study was to investigate hormonal and other factors associated with mammographic density during the menopausal transition and in postmenopause.
Design: Mammograms were obtained from 252 participants in the Melbourne Women's Midlife Health Project-a longitudinal population-based study that included annual interviews, blood collection, and physical measurements; 869 original films of the right craniocaudal view were digitized. Total area of the breast and the area of dense tissue were measured, and the percentage of mammographically dense tissue (PMD) was calculated. Data were analyzed using time-series regression models.
Results: Of the 252 women, 87% had more than one mammogram, and the mean age was 56.0 (SD 3.6) years (range 45-67); 129 women who had never used hormone therapy were included in the analyses. The mean nondense breast tissue area increased through the menopausal transition (P for trend=0.01), there was no significant trend in the mean dense breast tissue area, and mean PMD decreased (P for trend=0.004). Multivariate analysis showed that increasing age (P<0.005) and body mass index (BMI) (P<0.05), having had children (P<0.05), and higher than average free testosterone levels (P<0.05) (or lower than average sex hormone-binding globulin levels) were associated with increased area of nondense tissue. Increasing age (P<0.05) and BMI (P<0.05) were associated with decreased PMD. There was a tendency for higher than average free testosterone levels (P<0.07) and having had children (P=0.07) to be associated with lower PMD. After controlling for age, there were no significant associations with the area of dense tissue.
Conclusions: This longitudinal observational study has shown that after controlling for age, there was no apparent effect of menopausal change on the area of dense breast tissue. Aging and increasing BMI through the menopausal transition were associated with increased nondense breast tissue and explain a small, but statistically significant, portion of the variation in PMD tissue.