Menopausal HRT Series: Does estrogen cause breast cancer?

This post was written by our guest author, Dr. Tori Hudson, ND.

Menopausal hormone therapy prescribing is an essential skill in the care of women. It is imperative that all prescribers have a science-based approach to the benefits and risks of menopause hormone therapy (MHT). In my forty years of clinical practice as a licensed naturopathic physician and with a clinical practice in women’s health, I think I’ve seen every perimenopause/menopause issue, every possible evidence-based and historical use natural therapy, and likely every hormone prescription that women have been given, but I am still occasionally surprised and alarmed. My alarms go off when women are prescribed unusually high doses of estrogen and inadequate doses of a progestogen if they have a uterus. My alarm is heightened and my concern for her safety increases when, for example, she has been given a prescription by a practitioner who recently attended a pellet therapy seminar, and that seminar provided education which had the goal of practitioners becoming new or future users and prescribers of that proprietary method as well as seminar-owned medications. I’m also alarmed when I see practitioners recommending doses of hormones and prescribing patterns that change the calculation from benefit over risk to risk over benefit.

A classic example I’ve encountered is that providers are being taught that systemic estrogen therapy can be initiated at any age without risk, or that progesterone cream can be used for endometrial protection when systemic doses of estrogen are given, or supraphysiologic doses and high levels of estrogen that result from something like pellet therapy. But that’s just one scenario – don’t get me started on unproven regimens such as the “Wiley Protocol,” or doses of progesterone based on a saliva, urine, or serum test result, resulting in lower doses of progesterone given and the presumption that it’s the correct dose, despite prescribing estrogen and discounting the fact that she has a uterus. In this example, this progesterone dose is an unproven dose for her estrogen-stimulated uterus.

This Menopausal HRT blog series will focus on some classic myths that can lead to depriving women of hormones they may need, prescribing insufficient doses of progesterone in combination with systemic estrogen, timing of initiation of MHT, myths on discontinuation, and the subject of bioidentical hormones and compounding. Let’s start with myth #1.


Myth: Estrogen causes breast cancer

The primary fear that most women have about menopause hormone therapy (MHT) is that it will cause breast cancer. Not only does most data show that recommended menopausal estrogen doses alone do not cause breast cancer, but even recommended estrogen plus a progestin for 4 years or more appears to increase the risk ever so slightly – only one extra breast cancer per 1,000 women per year with estrogen and progestin. Estrogen and bio-identical progesterone, according to three observational French studies and a recent population-based study, do not increase the risk at all.

The studies on systemic estrogen alone range from:
1) A slight decreased risk (the original RCT from the Women’s Health Initiative (WHI))
2) A slight decreased risk from the 20-year WHI follow up
3) A slight increased risk in the Nurses Health Study
4) The recent population-based study in the next paragraph from the UK
5) Others with a null effect

The recent population-based case control study of women aged 50 years or older using data from the UK also highlights no increased risk with estrogen alone and shows a different risk dependent on type of progestogen with estrogen, as in the 3 observational French studies. Over a course of almost 20 years, there were 43,183 cases of breast cancer identified and matched to 431,830 women in a control group. Compared with women who never used MHT, its use was associated with a very slight increased risk of breast cancer. Compared with never users, estrogens alone were not associated with breast cancer (bio identical estrogens 1.04, animal derived estrogens 1.01, or both 0.96). Progestogens appeared to be differentially associated with breast cancer (micronized progesterone OR 0.99) (synthetic progestin OR 1.28).

While there are many papers that could be cited, the 2022 position statement from the North American Menopause Society (NAMS) provides an excellent summary of the overall issue of MHT and breast cancer, as well as other key issues.

For more information, I have written another blog post for Precision Analytical which can be read here. If you are interested in a book that lays out the science in a reliable and evidence-based manner, and spares you reading scores of articles, I suggest Estrogen Matters.

Follow along in the coming months to read more of my myth-debunking in this Menopausal HRT blog series.

Become a DUTCH Provider to learn more about how hormone testing can help inform comprehensive patient treatment plans.

This post was written by our guest author, Dr. Tori Hudson, ND.
Dr. Hudson is clinical adjunct professor at NUNM, Southwest College of Naturopathic Medicine, Bastyr University and the Canadian College of Naturopathic Medicine. Dr Hudson has been in practice for more than 36 years, is the medical director of “A Woman’s Time” in Portland, Oregon, co-owner and director of product research and education for VITANICA, and the program director for the Institute of Women’s Health and Integrative Medicine. She is also the founder and co-director of NERC (Naturopathic Education and Research Consortium), a non-profit organization for accredited naturopathic residencies. Dr. Hudson has been appointed as a faculty member of the Fellowship in Integrative Health and Medicine, Academy of Integrative Health & Medicine.

Learn More about Dr. Tori Hudson