The association between ovarian steroids and mammographic density parallels what is known about the effects of ovarian steroids and breast cell proliferation.43 Breast cell proliferation is higher in pre- than postmenopausal women and higher in women in the luteal than in the follicular phase of the menstrual cycle. In short, high estrogen/progesterone levels are associated with high amounts of breast cell proliferation.
A number of studies have examined what his-tological components are associated with mam-mographic densities. Although several studies have found an association between epithelial hyperplasia15,44-46 and mammographic densities, others have not.47-49 Oza and Boyd50 concluded that it was predominantly stromal proliferation that was associated with increased mammographic density. They further hypothesized that the complex interaction between breast stroma and epithelial tissue could explain why stromal proliferation shown by the mam-mogram is associated with an increased risk of epithelial malignancy.
Thus, it is likely that mammographic density is, if not a direct measure, at least a marker for breast cell proliferation. This means that reducing mammographic density may not only improve mammographic sensitivity but also ultimately reduce breast cell proliferation and breast cancer risk.
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