A link between progesterone and breast density

We have known of the increased risk of breast cancer associated with increased breast density since Wolfe's work published in 1976.  Many other reports have shown a strong association, and even stepwise increase of breast density to breast cancer risk.  An often quoted article from the New England Jr of Medicine in 2007, by Boyd, et al, compared women with density in <10% of the breast to those with density in 75% or more and found 4-5 times the number of breast cancers in the denser breasts.


Results from the WHI http://drwinsett.blogspot.com/2012/03/updated-menopausal-hormone-therapy.html#uds-search-results showed that women who took both estrogen and progesterone (EPT) had more breast cancers and further study of that group found that combined EPT users were also associated with increased mammographic density.


A recent study in Menopause (March 2102) looked into the link between progesterone and breast density.  Dr. Lee and a research team at University of Southern California reported on 280 postmenopausal women randomized to receive estrogen and progesterone therapy (EPT).  They observed that those taking the combined hormones (EPT group) had a post treatment increase in serum progesterone which was associated with increased mammographic density.  Furthermore, they noted that the higher the serum progesterone level, the greater the breast density as measured by mammogram.  Importantly, the higher progesterone levels (and higher mammographic density) was independent of increased estrogen levels.


Increases in mammographic density have been associated with more breast cancers, whether taking hormones or not.  Conversely decreased density has been associated with fewer breast cancers.  In review of the first International Breast Cancer Intervention Study using Tamoxifen to prevention breast cancers, the benefit of Tamoxifen was limited to the women who showed a significant decrease in breast density on mammography.


They looked at genetic variability in the progesterone receptor gene, but did not find evidence that genetic variation was involved in the density change, in this small study.


Still, it would seem that serial changes in breast density, judged mammographically, could be used to measure the risk or benefit of therapy, whether increasing risk with EPT or decreasing with Tamoxifen.  Maybe the answer is in the progesterone receptor and its variability of response to therapy.  Only further research may answer the question.


Nevertheless, I recommend that you know your breast density!




This content of this blog is intended as information and to provoke thoughtful discussion with your doctor.  It is not intended as personal medical advice. 




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