Hormones and Breast Cancer Risk: The Evidence Providers Need to Know
For decades, physicians were warned that hormone therapy causes breast cancer. That message still lingers in exam rooms today, keeping providers and patients hesitant. But when we look closely at the actual studies, a different story emerges: estrogen, progesterone, and testosterone each protect breast tissue when used appropriately in bioidentical form.
Estrogen: Protection, Not Promotion
The Women’s Health Initiative (WHI) changed clinical practice in 2002, but its data have often been misrepresented. With long-term follow-up, the WHI demonstrated that women with prior hysterectomy who received estrogen alone (CEE) had:
- 23% lower breast cancer incidence
- 44% lower breast cancer mortality
compared with placebo (Chlebowski et al., 2020).
Recent work reinforces this:
- Baik et al., 2024 studied over 10 million Medicare beneficiaries. Estrogen monotherapy beyond age 65 was associated with a 16% reduced risk of breast cancer, as well as reduced overall mortality and lower risks of multiple chronic conditions.
Clinical takeaway: Estrogen, especially when prescribed in bioidentical form and at physiologic doses, does not raise breast cancer risk — it can reduce it.
Progesterone: Bioidentical vs. Synthetic Progestins
The risk associated with “progestins” is not universal. Bioidentical progesterone behaves very differently from synthetic progestins like medroxyprogesterone acetate (MPA).
- A systematic review and meta-analysis (86,881 women) found that progesterone + estrogen therapy was associated with lower breast cancer risk compared with regimens using synthetic progestins (RR 0.67; 95% CI 0.55–0.81) (Stute et al., 2016).
- The French E3N cohort demonstrated that women on estradiol + natural progesterone had no increased breast cancer risk, while women on estradiol + synthetic progestins had significantly higher risk (Fournier et al., 2007).
Mechanistically, progesterone supports cell differentiation, promotes apoptosis, and reduces breast tissue inflammation — protective processes that synthetic progestins do not replicate.
Clinical takeaway: Bioidentical progesterone protects the breast, while synthetic progestins are the culprits driving risk.
Testosterone: An Overlooked Protector
Testosterone is often ignored in breast cancer discussions, but it plays a vital protective role.
- In a prospective 10-year cohort, women treated with subcutaneous testosterone implants had a lower-than-expected incidence of invasive breast cancer compared with SEER population data (Glaser et al., 2019).
- Mechanistically, testosterone’s metabolite 3β-adiol activates estrogen receptor beta (ERβ), a receptor known to suppress tumor growth and regulate cell proliferation (Wu et al., 2011).
Clinical takeaway: Adequate testosterone is breast-protective, opposing unchecked proliferation and engaging tumor-suppressive pathways.
Dispelling the Myth
The old narrative that “hormones cause breast cancer” is not supported by current evidence. The data are clear:
- Estrogen lowers breast cancer incidence and mortality in randomized trials.
- Progesterone is protective in its natural form, unlike synthetic progestins.
- Testosterone helps regulate proliferation and supports tumor-suppressive signaling.
When prescribed thoughtfully in bioidentical form, hormones do not raise breast cancer risk — they protect against it.
The Bigger Picture
It is time to stop denying women the broad and well-documented benefits of bioidentical hormone therapy. Beyond breast protection, hormones prevent bone loss and fractures, protect cardiovascular health, reduce the risk of diabetes and dementia, improve mood and cognition, support weight management, and are linked to greater longevity and quality of life. For too long, fear has outweighed facts. The science now demands we dispel the myths and give women access to therapies that restore vitality and protect long-term health.
Schedule a Strategy Call
Understanding the evidence is one thing—knowing how to apply it in practice is another. If you’re ready to confidently address patient concerns about hormones and breast cancer,
and to learn how BHRT can be integrated safely and effectively into your clinic, schedule a 1:1 strategy call with one of our Provider Education Specialists.
They’ll walk you through:
- How to talk to patients about hormone safety and breast cancer risk
- The best training pathway for you and your team
- Practical tools to expand services, retain patients, and grow your practice
👉 Schedule Your Strategy Call Today »
References
- Chlebowski RT, Anderson GL, Aragaki AK, et al. Association of menopausal hormone therapy with breast cancer incidence and mortality during long-term follow-up of the Women’s Health Initiative randomized clinical trials. JAMA. 2020;324(4):369-380. doi:10.1001/jama.2020.9482.
- Baik SH, Baye F, McDonald CJ. Use of menopausal hormone therapy beyond age 65 years and its effects on women’s health outcomes by types, routes, and doses. Menopause. 2024;31(5):363-371. doi:10.1097/GME.0000000000002335.
- Fournier A, Berrino F, Clavel-Chapelon F. Unequal risks for breast cancer associated with different hormone replacement therapies: results from the E3N cohort study. Breast Cancer Res Treat. 2007;107(1):103-111. doi:10.1007/s10549-007-9523-x.
- Stute P, Wildt L, Neulen J. Progesterone versus synthetic progestins and the risk of breast cancer: a systematic review and meta-analysis. Syst Rev. 2016;5:121. doi:10.1186/s13643-016-0294-5.
- Glaser R, York AE, Dimitrakakis C. Incidence of invasive breast cancer in women treated with testosterone implants: a prospective 10-year cohort study. BMC Cancer. 2019;19:1271. doi:10.1186/s12885-019-6457-8.
- Wu X, Subramaniam M, Grygo SB, et al. Estrogen receptor-β sensitizes breast cancer cells to the anti-estrogenic actions of endoxifen. Breast Cancer Res. 2011;13(2):R27. doi:10.1186/bcr2844.
