Breast cancer touches almost every family in some way. In Canada, it is the second most common cancer among women after non-melanoma skin cancer. About 1 in 8 Canadian women will develop breast cancer in their lifetime.
That statistic can feel frightening, but it is also a reminder that breast cancer risk is not caused by one single choice, one medication, or one lifestyle factor. Every woman has some baseline risk simply because breast tissue is exposed to hormones and changes over time. Age, genetics, family history, reproductive history, alcohol intake, body weight, and physical activity can all influence that baseline risk.
Hormone replacement therapy, now more accurately called menopausal hormone therapy (MHT), is something many women consider during the menopause transition and are learning lots about now through social media and podcasts.
As a Naturopathic Doctor and Menopause Society Certified Practitioner, one of the most common questions I hear from women considering MHT is: “Does hormone therapy have any risks?” My answer is usually that almost every effective treatment in medicine carries some potential risk.
The more useful questions are:
- How large is the risk for me?
- How does it compare with the other risks in my life?
- And how does it weigh against the impact my symptoms are having right now, and the benefits I could gain from treatment?
This is why personalized care matters so much. Women’s health is complex, and decisions about hormone therapy deserve more than a rushed five-minute conversation. They call for time to review your personal and family history, your symptoms, your goals, and your values, so that together we can find the approach that is right for you.
Breast Cancer Risk Is Like Filling a Bucket
Think of breast cancer risk as a bucket that starts with some water already in it. Every woman’s bucket begins at a different level because of factors they cannot control, such as:
- Age
- Family history
- Inherited genetic variants
- Breast density
Over a lifetime, certain factors may add a little more water to the bucket. Others may help prevent it from filling as quickly.
For example, regular physical activity is associated with a lower breast cancer risk. A meta-analysis of prospective studies found that women with the highest activity levels had about a 12% lower breast cancer risk than those with the lowest activity levels.
Alcohol use, particularly higher intake, can add to risk. In a major evidence review, each additional 10 g (~ 1 glass of wine) of alcohol daily was associated with approximately a 5% increase in premenopausal breast cancer risk and a 9% increase in postmenopausal breast cancer risk. The risk increases exponentially with the amount of alcohol consumed daily, approximately 3 to 4 drinks daily was associated with a 32% increase.
Postmenopausal obesity and low physical activity are also important modifiable contributors.
The point is not to blame women for their risk, or to imply that breast cancer can always be prevented. It cannot. The point is to make decisions with perspective, rather than fear.
Hormone therapy and breast cancer risk
MHT can be another factor in the bucket, but its effect depends on the specific hormones used, whether a progestogen is required, the duration of use, and a woman’s individual health history.
Systemic MHT is the most effective treatment for bothersome hot flashes and night sweats related to menopause and is also highly effective at treating other menopausal symptoms such as:
- Brain fog
- Insomnia
- Mood changes
- Joint pain
- Genitourinary changes
The North American Menopause Society estimates that the breast cancer risk attributable to hormone therapy is rare, at fewer than one additional case per 1,000 women per year of use, or approximately three additional cases per 1,000 women using conjugated estrogen plus medroxyprogesterone acetate for five years (this is based on old study using non-bioidentical forms of HRT). To put that in perspective, about 3 in every 1,000 women in their 50s will be diagnosed with breast cancer in any given year, whether or not they use hormone therapy.
If those same 1,000 women each drank about two glasses of wine a day for five years, we would expect roughly three to four additional cases, which is about the same as with combined hormone therapy. Even one drink a day would add about one to two cases over that time.
On the other side of the scale, if those 1,000 women were among the most physically active, we would expect about two fewer cases over five years. In other words, the added risk from hormone therapy is in the same range as everyday choices many women make without a second thought, and regular movement and drinking less can help balance it.
The Canadian guideline notes that breast cancer risk varies according to the type of MHT and duration of treatment. The greatest risk is seen with combined estrogen plus a synthetic progestin (such as medroxyprogesterone acetate -MPA). Estrogen-only therapy for women who do not have a uterus carries little to no added risk.
Observational studies suggest that bioidentical micronized progesterone (prometrium) may carry a lower breast cancer risk than synthetic progestins such as MPA. Breast cancer risk appears similar whether estrogen is taken as a pill or through the skin (patch, gel etc) although transdermal estrogen has the advantage of a lower risk of blood clots and stroke.
It is also important to remember the other side of the conversation. For some women, hormone therapy is truly life-changing. Relief from relentless hot flashes, sleepless nights, brain fog, and mood changes can mean returning to work, relationships, and daily life with confidence. When started in the right person at the right time, usually before age 60 or within 10 years of menopause, hormone therapy also helps protect against bone loss and fractures from osteoporosis. It has been linked with a lower risk of developing type 2 diabetes and supports cardiovascular health.
Choosing hormone therapy is not about ignoring risk. It is about weighing a small, measurable risk against benefits that can be very real as every woman has a unique bucket and various severity of menopausal symptoms.
What About Vaginal Estrogen?
Low-dose vaginal estrogen is different from systemic MHT. It is used for genitourinary syndrome of menopause, which can include:
- Vaginal dryness & burning
- Pain with sex
- Urinary urgency, recurrent urinary symptoms & urinary tract infections.
Low-dose vaginal estrogen is designed to act mainly in local vaginal and vulvar tissues, rather than throughout the body. Current guidance describes low-dose vaginal estrogen as effective for these symptoms, with minimal systemic absorption.
Research summarized in the genitourinary syndrome of menopause position statement found no association between vaginal estrogen use and breast cancer risk in the observational evidence reviewed.
For women with a personal history of breast cancer, the conversation deserves extra care. The Society of Obstetricians and Gynaecologists of Canada states that systemic MHT is contraindicated after breast cancer. However, low-dose vaginal estrogen may be considered for breast cancer survivors when non-hormonal measures have not adequately relieved symptoms, with shared decision-making and involvement of the oncology team.
The Main Takeaways
Breast cancer risk is not an all-or-nothing issue. Every woman has some baseline risk, and that risk is shaped by many factors over time.
Systemic MHT can slightly increase breast cancer risk in some settings, and the increase is generally small in absolute terms, but it should be discussed openly with your prescribing practitioner.
MHT-related risk should be considered alongside other modifiable influences, including alcohol use, body weight after menopause, and physical activity.
Low-dose vaginal estrogen is not the same as systemic MHT. It has minimal systemic absorption and is generally regarded as a low-risk option for vaginal and urinary menopausal symptoms, including in carefully selected breast cancer survivors after appropriate discussion with their care team.
Shared Decision Making
Shared decision-making means you and your practitioner decide together whether menopausal hormone therapy fits you, weighing the best available evidence against your own goals, values and concerns. The conversation should cover the following:
- How much your symptoms affect your daily life
- Your personal and family history (including breast cancer)
- Your age and time since menopause
- Your personal values.
- The type, dose and route of any hormone therapy
- The alternatives
- A plan to review the decision as your needs change.
For guidance specific to you, look for a clinician with menopause expertise, such as a Menopause Society Certified Practitioner (MSCP), whom you can find through The Menopause Society’s practitioner directory. All of the female naturopathic doctors at NutriChem have their MSCP certification.
The goal is not to make women afraid of hormones, nor to suggest that every woman should use them. The goal is informed, individualized care: understanding personal risk, recognizing the impact of menopausal symptoms, and choosing an approach that supports overall health and quality of life.
References
Chlebowski, R. T., Anderson, G. L., Aragaki, A. K., Manson, J. E., Stefanick, M. L., Pan, K., et al. (2020). 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, 324(4), 369-380.
Chlebowski, R. T., Anderson, G. L., Manson, J. E., et al. (2023). The Women’s Health Initiative randomized trials of menopausal hormone therapy and breast cancer: Findings in context. Menopause, 30(3), 249-261.
World Cancer Research Fund International. (2017). Diet, nutrition, physical activity and breast cancer. World Cancer Research Fund International.
World Cancer Research Fund International. (2025). Dietary and lifestyle patterns for cancer prevention: Evidence and recommendations from CUP Global. World Cancer Research Fund International.
Pizot, C., Boniol, M., Mullie, P., Koechlin, A., Boniol, M., & Autier, P. (2016). Physical activity, hormone replacement therapy and breast cancer risk: A meta-analysis of prospective studies. European Journal of Cancer, 52, 138-154.
Rock, C. L., Thomson, C., Gansler, T., et al. (2020). American Cancer Society guideline for diet and physical activity for cancer prevention. CA: A Cancer Journal for Clinicians, 70(4), 245-271.
Cancer Australia. (n.d.). Modifiable factors: Breast cancer risk factors. Cancer Australia.
