Another day, another splashy headline about hormone therapy and breast cancer.
This time it’s from the NIH and published in Lancet Oncology: “Breast cancer risk in younger women may be influenced by hormone therapy.” The media jumped on it, suggesting that women under 55 who use hormone therapy are at increased risk.
Cue the fear. Again.
But let’s be clear: this study tells us absolutely nothing new. This study showed the same results as the WHI. Estrogen + synthetic progestin (NOT progesterone) increases breast cancer risk. Estrogen alone lowers it. Y’all….it’s NOT estrogen’s fault (again)!
Let’s break it down so you can make decisions based on facts, not fear.
WHI: The Study That Changed Everything… and Created Mass Confusion
In the early 2000s, the WHI studied two groups of women:
- Women with a uterus received conjugated equine estrogens (CEE) + medroxyprogesterone acetate (MPA)—a synthetic progestin.
- Women without a uterus received CEE alone.
When the trial was halted in 2002, the media exploded with claims that estrogen causes breast cancer. What didn’t make headlines? The nuance:
- The estrogen-only group had a lower risk of breast cancer.
- The increased risk came from the combination of estrogen + synthetic progestin, and even then, it was relatively small.
- Most participants were in their 60s—not the age group where hormone therapy is usually started.
The fallout was devastating. Millions of women were pulled off their hormones. Doctors became afraid to prescribe. And the idea that “estrogen causes cancer” got cemented in public consciousness, even though the science told a different story. AND we’re STILL dealing with it!
What the NIH Study Actually Says
This latest NIH study simply zooms in on women aged 16-54 (mean age of 42 years old).
The researchers conducted a large-scale analysis that included data from more than 459,000 women under 55 years old across North America, Europe, Asia, and Australia. Women who used estrogen-only therapy had a 14% reduction in breast cancer incidence compared to those who never used hormone therapy. Notably, this protective effect was more pronounced in women who started hormones at younger ages or who used it longer.
In contrast, women using estrogen+progestin experienced a 10% higher rate of breast cancer compared to non-users, with an 18% higher rate seen among women using combo therapy for more than two years relative to those who never used the therapy.
According to the authors, this suggests that for estrogen/progestin users, the cumulative risk of breast cancer before age 55 could be about 4.5%, compared with a 4.1% risk for women who never used hormone therapy and a 3.6% risk for those who used estrogen alone.
And here’s the kicker: they still didn’t differentiate between synthetic progestins like medroxyprogesterone acetate and bioidentical progesterone. That distinction makes all the difference in real-world risk—and real-world outcomes.
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The Real Problem Isn’t Estrogen—It’s the Type of Progestin
One of the biggest misconceptions in hormone therapy is that “progesterone” is the problem. But it’s not that simple.
The WHI used medroxyprogesterone acetate (MPA)—a synthetic progestin. That’s not the same as micronized progesterone, which is bioidentical (chemically identical to what your body makes) and metabolized very differently.
Here’s what the research shows:
- The E3N French cohort study followed nearly 100,000 women and found that estrogen + synthetic progestins increased breast cancer risk. But estrogen + micronized progesterone or dydrogesterone did not (Fournier et al., 2008).
- A 2016 paper in Climacteric confirmed that micronized progesterone has a much safer profile than synthetic progestins (Stute et al., 2016).
- Short-term use (<5 years) of estradiol + micronized progesterone shows no increased breast cancer risk (Chlebowski et al., 2010).
That’s why in my practice, I encourage women to ask their provider for topical estrogen and oral micronized progesterone when appropriate.
Estrogen Alone? Surprisingly Protective
If you’ve had a hysterectomy and are using estrogen-only therapy, here’s the good news: it’s not only safe—it’s been shown to be protective when it comes to breast cancer.
The WHI’s long-term follow-up showed that women on CEE alone had a 23% lower risk of breast cancer compared to placebo (Chlebowski et al., 2010). And other studies back this up.
Unfortunately, most women never hear this part of the story. The myth that “any hormone equals cancer” is deeply embedded—and it’s time we set the record straight.
And let’s not lose sight of the fact that adding progesterone even after the uterus is gone provides benefits far beyond uterine protection (like sleep, anxiety, bone health and nerve heath). Your body has progesterone receptors all over it!
Let’s Get Real
Headlines sell. But when you boil it all down, the increase in breast cancer risk from synthetic progestins is comparable to or lower than the risks associated with:
- Drinking 1 glass of wine daily
- Gaining 20 pounds after menopause
- Not exercising regularly
Funny how no one’s writing headlines about that.
So, What’s the Real Takeaway?
The Bottom Line
This is why working with a provider who understands the science—and treats you as an individual—is so important.
Hormone therapy isn’t just about managing hot flashes and vaginal dryness. It’s about protecting brain health, bone density, cardiovascular function, sleep quality, and your overall healthspan. For the right woman, at the right time, in the right form—it can be life-changing.
So don’t let scary headlines put you off. Ask better questions. Get complete answers. And remember that you get to make informed, empowered decisions about your body.
References
Chlebowski, R. T., Anderson, G. L., Aragaki, A. K., Manson, J. E., Stefanick, M. L., Pan, K., … & Prentice, R. L. (2010). Estrogen plus progestin and breast cancer incidence and mortality in postmenopausal women. JAMA, 304(15), 1684–1692. https://doi.org/10.1001/jama.2010.1500
Fournier, A., Berrino, F., & Clavel-Chapelon, F. (2008). Unequal risks for breast cancer associated with different hormone replacement therapies: results from the E3N cohort study. Breast Cancer Research and Treatment, 107(1), 103–111. https://doi.org/10.1007/s10549-007-9523-x
Stute, P., Wildt, L., Neulen, J., & Cagnacci, A. (2016). Micronized progesterone: breast cancer risk in hormone therapy. Climacteric, 19(4), 316–318. https://doi.org/10.3109/13697137.2016.1173900
Vinogradova, Y., Coupland, C., & Hippisley-Cox, J. (2020). Use of hormone replacement therapy and risk of breast cancer: nested case-control studies using the QResearch and CPRD databases. BMJ, 370, m3873. https://doi.org/10.1136/bmj.m3873
National Institutes of Health. (2025, June 30). Breast cancer risk in younger women may be influenced by hormone therapy. https://www.nih.gov/news-events/news-releases/breast-cancer-risk-younger-women-may-be-influenced-hormone-therapy
Dr. Anna Garrett is a menopause expert and Doctor of Pharmacy. She helps women who are struggling with symptoms of perimenopause and menopause find natural hormone balancing solutions so they can rock their mojo through midlife and beyond. Dr. Anna is the author of Perimenopause: The Savvy Sister’s Guide to Hormone Harmony. Order your copy at www.perimenopausebook.com.
Dr. Anna is available for 1-1 consultation. Find out more at www.drannagarrett.com/lets-talk
