Progesterone: The Breast Cancer Shield

by | Jul 7, 2020 | Articles, Cancer, Conditions, Hormone Replacement, Women's Health

Breast cancer is understandably the greatest concern of women who are considering hormone replacement therapy (HRT) and yet the media and medical community have only confused the issue with blanket statements regarding risk and a sorry lack of specifics. Before deciding whether HRT is right for you it is essential to learn more about the risk of cancer.

Guilt by association – Provera is NOT progesterone

Results from the Women’s Health Initiative (WHI) show an increased risk of breast cancer with the use of the drug called Provera, even for several years after stopping it, but then (the makers of Provera reassure us) the risk drops off with time. The original WHI data showed a 26% increased risk for invasive breast cancer in women taking the mixture of Premarin and Provera.

Provera (medroxy-progesterone) is a drug that is similar to our native progesterone – not identical, merely similar, like hundreds of chemical compounds that will stimulate progesterone receptors in the body. These chemicals are called “progestogens” and synthetic drugs in this category are known as “progestins”.

If one brand of automobile is defective and killing people as a result should we then cast blame on the entire auto industry and recall every brand of automobile? That is precisely what is happening in the world of HRT!  A bioidentical hormone has a molecular structure that is 100% identical to the hormone molecule the body makes. Progesterone is bioidentical, Provera is not, and this does make a difference.

There are numerous reviews that suggest progesterone has a protective effect on breast tissue. Low levels of progesterone have been associated with increased risks of breast cancer. Progesterone, and NOT progestins, provides a control mechanism to regulate the proliferative effects of estrogen. This means it prevents cancer.

A French study showed no increased risk of breast cancer in women using progesterone cream topically, and actually a reduced risk when adding a progesterone capsule.  Another French study showing no increased breast cancer risk when taking progesterone as opposed to synthetic progestins.

The largest study to date that most conclusively addresses the debate over progesterone and breast cancer is the French E3N-EPIC (European prospective investigation into cancer and nutrition) which is a cohort study looking at over 50,000 women. It showed the same results as the WHI in women using synthetic progestins, that is a 26% increased risk for invasive breast cancer. But, it showed a 10% decreased risk for breast cancer in women using progesterone – a 10% decrease!

I am not aware of any prospective trials that assess the safety of bioidentical progesterone with respect to breast cancer. Distinguishing causality from correlation cannot usually be done with results of a cohort study alone, but the above referenced cohort studies provide a very strong case for the safety of bioidentical progesterone.

Lowering risk of breast cancer

There are many proven methods to reduce the risk of breast cancer. Start with diet and include plenty of cancer fighting fruits and vegetables, preferably raw and organic. A raw foods diet, especially with juicing, is particularly helpful. Avoid packaged over-processed foods in general. Eliminate sugar and high glycemic carbs. Shun trans-fats and hydrogenated oils. Limit alcohol to less than two drinks daily. I have patients that have reversed cancer with diet alone… There is no point in glossing over how important diet is in cancer prevention.

Regular exercise lowers the chance of breast cancer about 10-20%.  Avoiding xenoestrogens, which are chemicals in our environment that act like strong estrogens in the body, also lowers risk of cancer.

Inflammation plays a role in cancer. Part of the benefit of good diet is to control inflammation. Supplements such as curcumin, green tea, boswellic acid, ginger, and pomegranate are well known for their anti-inflammatory and anti-cancer properties. These plant compounds, called polyphenols regulate cell growth and metabolism. Some of them encourage the programmed self-destruction of cancer cells, called “apoptosis”. Others control oxidation, block new blood vessel growth to cancer or help slow metastases.

Women with the lowest vitamin D levels have higher rates of breast cancer. By blocking signals that encourage cancer cell growth, turning on signals that inhibit cancer cell growth, and playing a role in the cellular life cycle, vitamin D has several mechanisms to improve cancer risk. The only way to know how much vitamin D to take is to get serial blood levels over a few years. A typical dosage is 2000-5000 units / day and D3 is the best form to supplement.

Fermented soy is another food that lowers the risk of breast cancer.  This is due to soy’s ability to stimulate the estrogen receptors that down-regulate breast cancer growth while effectively “blocking” the receptors that promote cancer when they are exposed to our own estrogens or foreign chemicals that stimulate estrogen receptors.

So what about HRT?

The current conventional medical recommendations are to not take hormone replacement and if necessary to treat menopausal symptoms then to quit HRT as soon as possible. This is based solely on the studies showing Provera causes cancer, heart attack, stroke and blood clots. I would agree with not taking synthetic hormone “look-alike” drugs and I’ve not prescribed Provera in over 20 years. Frankly, I think it should be removed from the market.

Bioidentical HRT is an established, researched science that is truly about preventing disease and maintaining quality of life. Bioidentical HRT is very effective at providing symptom relief for acute menopausal symptoms as well as preventing many symptoms and diseases associated with aging.

The best route of administration for estrogen and progesterone is to avoid oral capsules.  This is because oral capsules once absorbed go directly to the liver for metabolism, known as “first pass metabolism”.  With oral estrogen this leads to risks of blood clots, gallbladder sludge and poor metabolites.  With oral progesterone it leads to very sedating metabolites, less progesterone to actually get into tissues for protection and with doses over 100mg or so poor metabolites.  We prefer topical or sublingual hormone administration as the safest and most effective method for HRT.

Testing Progesterone Metabolites

Good = 4-pregnenes (3aHP and 20aHP) – 3α- Dihydroprogesterone and 20α- Dihydroprogesterone

Bad = 5-pregnanes (5aHP) – pregnanediol, allopregnanolone, allopregnanediol

Good ratio = high 4P / 5P rati0

Further reading on progesterone and estrogen metabolites and cancer risk

Progesterone Use as Hormone Replacement Therapy

Progesterone Metabolites in Breast Cancer

Estrogen Metabolite Ratios: Time for Us to Let Go


Scott Rollins, MD, is Board Certified with the American Board of Family Practice and the American Board of Anti-Aging and Regenerative Medicine.  He specializes in bioidentical hormone replacement for men and women, thyroid and adrenal disorders, fibromyalgia and other complex medical conditions.  He is founder and medical director of the Integrative Medicine Center of Western Colorado ( and Bellezza Laser Aesthetics (   Call (970) 245-6911 for an appointment or more information.

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