Bioidentical (Natural) Hormones and Breast Cancer Risk

hormonebreastcancerLarge French Studies Show No Increased Risk of Breast Cancer for Users of Bioidentical Hormones

The good news about large epidemiological (population) studies in much of Europe is that socialized medicine allows for easier tracking of many participants over many years. In the E3N French Women Prospective study, tens of thousands of women are being followed over many years. One arm of the study, lead by Agnès Fournier, is examining the effects of HRT over time.

The first results were published in 2005. According to the authors, “…the main specificity of the French cohort is that 83% of the combined HRT users were receiving mostly or exclusively a transdermal estradiol gel formulation, and the progestin was oral micronized progesterone in 58%, while MPA [a synthetic progestin] users were less than 3%.” Oral micronized progesterone is bioidentical, natural progesterone, which is what most French women use, rather than the synthetic progestins. The conclusion of the study was that, “When both duration of use and the last period of use were analyzed together, no significant increase in breast cancer incidence was observed in any of the four subgroups considered,” and “From internal analysis, there was no significant increase in the risk of breast cancer related to use of the specific type of HRT most prescribed in France.”

In other words, women using synthetic HRT had an increased risk of breast cancer, while bioidentical hormone users had the same breast cancer risk as women who did not take hormones at all. This part of the study involved 54,548 postmenopausal women who had not been on any kind of HRT for at least a year before entering the study. The average age was 53, and the study lasted for almost 6 years. Compared to women who had never used HRT, those using estrogen plus synthetic progestins had a 40% increased risk of breast cancer, while those using estradiol plus progesterone (e.g. bioidenticals) had a 10% decreased risk of breast cancer.

In January 2008, with eight years of follow-up, data was released from E3N showing that women using synthetic HRT had a 60% higher risk of cancer, while women using bioidenticals still had the same risk as women using no HRT of any kind.

A literature review in the prestigious journal Maturitas: The European Journal of Menopause concluded, “…a growing literature suggests that the progestins used in association with estrogens may not be equivalent. Recent evidence indeed shows that natural progesterone displays a favorable action on the vessels and on the brain, while this might not be true for some synthetic progestins. Compelling indications also exist that differences might also be present for the risk of developing breast cancer, with recent trials indicating that the association of natural progesterone with estrogens confers less or even no risk of breast cancer as opposed to the use of other synthetic progestins. In conclusion, while all types of hormone replacement therapies are safe and effective and confer significant benefits in the long-term when initiated in young postmenopausal women, in specific clinical settings the choice of the transdermal route of administration of estrogens and the use of natural progesterone might offer significant benefits and added safety.”

For interested health care professionals and other assorted geeks, the Maturitas review cited below is a comprehensive and organized analysis of much of the research on bioidenticals vs. synthetic hormones, and can be downloaded for a fee at the Maturitas website.


Fournier et al, “Use of different postmenopausal hormone therapies and risk of histology- and hormone receptor-defined invasive breast cancer,” J Clin Oncol 2008 Mar 10;26(8):1260-8.

Fournier et al,Unequal risks for breast cancer associated with different hormone replacement therapies: results from the E3N cohort study,” Breast Cancer Res Treat 2008 Jan;107(1):103-11.

Fournier et al, “Breast cancer risk in relation to different types of hormone replacement therapy in the E3N-EPIC cohort,” Int J Cancer 2005 Apr 10;114(3):448-54.

L’Hermite et al, “Could transdermal estradiol+progesterone be a safer postmenopausal HRT? A review,” Maturitas 2008 Vol 60, Issue 3, Pages 185-201.

You can find out more about how to use bioidentical hormones wisely by reading What Your Doctor May Not Tell You about Menopause, or Dr. John Lee's Hormone Balance Made Simple.

You can find out more about hormones and breast cancer risk by reading What Your Doctor May Not Tell You about Breast Cancer.

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