MHT and Breast Cancer. What the Current Evidence Actually Says.

For most women, the question of whether MHT will increase their breast cancer risk is the question that decides everything.

Hot flushes. Broken sleep. Brain fog. Joint pain. Low mood.

None of it weighs as heavily as four words. Will it cause cancer.

Specifically, breast cancer. Because almost every woman knows another woman who has had it. Because the fear of it has been built into how we talk about hormones for two decades. And because saying yes to MHT can feel, at the moment of decision, like saying yes to a risk you did not have to take.

The fear is real, and it deserves a clear answer rather than a reassuring or dismissive one.

The current evidence shows that MHT and breast cancer is not a single risk you accept or refuse. It is a small, specific risk that depends on what type of MHT, what type of progestogen, how long you take it, and what your individual risk profile already is. For some women, the risk is essentially neutral. For others, it is small but real and meaningful. For very few, it is enough to make MHT inappropriate.

This blog walks you through what the evidence actually says, so you can take the question into a GP conversation knowing what is on the table.

The fear of breast cancer is valid. I am sure that, like me, you know women who have undergone the difficult treatment process for breast cancer. Perhaps, like me, you know women who have died far too young because of breast cancer.

When I considered MHT for myself, I did not link breast cancer to it. As a nurse, with a lifetime in healthcare, I am well aware that all medication has both desired effects and unintended consequences. Some are minor. Others are life-altering.

But no sooner had I started looking into MHT than I was hearing about breast cancer risk. Loudly. Repeatedly. From women whose information often dated back to 2002, even when they could not name the source.

I was directed to a book called Estrogen Matters by Dr Avrum Bluming. For me, it helped put the risk in context. Since then, I have continued to study and read, and what I have learned is that the breast cancer story is genuinely nuanced. The same evidence base also shows that MHT may reduce the risk of some other cancers, including endometrial cancer when combined therapy is used [10], and colorectal (bowel) cancer [11].

That is the conversation worth having. Not whether MHT is dangerous. But what the evidence, all of it, actually shows.

Where did the breast cancer fear come from?

Most of the fear traces to one study and one set of headlines.

In 2002, the Women's Health Initiative, the largest trial of MHT ever undertaken, published its first major results. The combined oestrogen-plus-progestin arm of the study reported an increased risk of breast cancer, and the trial was stopped early [1].

The headline number, a percentage increase in breast cancer risk, became the single thing most women remembered about MHT for the next twenty years.

The previous blog in this series goes into the WHI study in more detail, including the full prescribing data and the relative-versus-absolute-risk framing.

[H3 BOLD] What got lost in those headlines were three things that matter enormously when you sit down with a current GP and ask the question.

The first is that the WHI study used hormones that are no longer the modern Australian first-choice for prescribing. Different drug. Different molecule. Different delivery method. The oestrogen was conjugated equine oestrogen (a mixture of oestrogens derived from pregnant mare urine), and the progestogen was medroxyprogesterone acetate, a synthetic. Australian first-line MHT today is body-identical oestradiol, usually delivered through the skin, with micronised progesterone where progesterone is needed.

The second is that the average woman in the WHI study was 63 years old, with many participants more than ten years past menopause, and a significant number with cardiovascular risk factors before they ever started MHT [2]. This is not the woman in her early fifties starting MHT for symptoms.

The third is the difference between relative risk and absolute risk. The WHI headlines focused on relative risk, the percentage increase compared to women not taking the treatment. Most women never heard the absolute numbers, the actual additional cases per thousand women per year, which were far smaller than the headline percentages suggested.

What are the two types of MHT, and why does it matter for breast cancer?

Modern MHT comes in two main forms, and the breast cancer signal is meaningfully different between them.

Oestrogen-only MHT

Oestrogen-only MHT is prescribed for women who do not have a uterus, usually because of a hysterectomy. These women do not need progesterone, because the role of progesterone in MHT is to protect the lining of the uterus from over-stimulation by oestrogen.

Combined MHT

Combined MHT is oestrogen plus a progestogen. It is prescribed for women who still have a uterus. The progestogen is added specifically to protect the uterine lining.

This distinction matters because the breast cancer signal looks different depending on which type of MHT a woman is on.

What does the evidence say about oestrogen-only MHT?

This is one of the most under-publicised findings in the entire MHT literature.

The WHI oestrogen-only arm followed women who had had a hysterectomy and were given conjugated equine oestrogen alone. On extended long-term follow-up, the data did not show an increased risk of breast cancer. They showed the opposite [3].

Dr Avrum Bluming, a medical oncologist whose practice was 60% devoted to breast cancer, summarised the position directly in CA: A Cancer Journal for Clinicians in 2024: "According to WHI's own data, estrogen alone significantly decreases the risk of breast cancer development (by 23%) and the risk of breast cancer death (by 40%), crucial information for women who have had hysterectomies" [4].

The Australasian Menopause Society, and the British Menopause Society, both reflect this in their current information sheets on MHT and breast cancer risk [5,6].

For women without a uterus considering oestrogen-only MHT, the breast cancer fear that may have shaped the decision is no longer supported by the current evidence.

What does the evidence say about combined MHT?

Combined MHT, oestrogen with a progestogen, does carry a small additional breast cancer risk over years of use. Acknowledging this honestly matters.

The size of the increase is what matters.

For a typical woman in her early fifties starting combined MHT for symptoms, the additional risk per year is small in absolute terms. The exact number depends on the specific formulation, dose, and duration of use [5,6].

To put that in context, that level of additional risk is in a similar range to the additional risk associated with:

- Drinking two or more alcoholic drinks a day

- Carrying significant excess weight (high BMI, particularly post-menopause)

- A sedentary lifestyle

These are everyday risks women navigate without anxiety. The point is not to dismiss the additional MHT-associated risk. The point is to put it alongside the risks women are already living with, so the comparison is honest. The fear that has stopped a generation of women from considering combined MHT has rarely been weighed against the lifestyle risks that surround them every day.

Does the type of progestogen matter?

Yes. And this is where current Australian practice has shifted significantly.

The progestogens used in older combined MHT, including the medroxyprogesterone acetate used in WHI, are synthetic compounds that act on progesterone receptors but are structurally different to the progesterone the body produces.

Micronised progesterone, sold in Australia as Prometrium, is body-identical, meaning it has the same chemical structure as the progesterone the body produces.

A 2016 systematic review and meta-analysis, looking specifically at the breast cancer risk of body-identical micronised progesterone compared with older synthetic progestins, found a relative risk of 0.67 with micronised progesterone, meaning roughly a third less breast cancer risk compared with older synthetic options [7].

The E3N cohort study, a major French observational study of more than 80,000 women, found similar patterns. Combined MHT using micronised progesterone showed a meaningfully smaller breast cancer signal than combined MHT using older synthetic progestins, particularly within the first five years of use [8].

The Australasian Menopause Society currently acknowledges this difference in its position statement on MHT and breast cancer, noting that body-identical micronised progesterone may be associated with a more favourable breast cancer profile compared to older synthetic options [9].

For women starting combined MHT in Australia today, micronised progesterone is the body-identical choice. This is a question worth raising in your GP conversation.

What about endometrial and bowel cancer?

This is part of the conversation that rarely makes it into the breast cancer discussion, and it should.

The current evidence shows that combined MHT (oestrogen plus progestogen) does not increase, and may actually reduce, the risk of endometrial cancer. A 2020 systematic review in Cancers, looking at 31 studies and over 21,000 women, found that continuous combined MHT was associated with a reduced risk of endometrial cancer in the majority of studies analysed [10]. This is the protective role of progesterone working as intended.

The risk picture for oestrogen-only MHT in women with a uterus is the opposite. Unopposed oestrogen does increase endometrial cancer risk, which is exactly why progesterone is added when a woman still has a uterus.

For colorectal (bowel) cancer, the evidence points toward a reduction with MHT. A large Swedish cohort study of 290,186 women published in the European Journal of Cancer in 2017 found that MHT was associated with a reduction in gastrointestinal cancers, including colon cancer (standardised incidence ratio 0.90) [11]. The Australian Menopause Alliance also notes the favourable picture for colorectal cancer in its consumer information [12].

None of this is a reason on its own to take MHT. But it does belong in the picture, alongside the breast cancer conversation, when the question is whether MHT is safe.

What about a family history of breast cancer?

Many women assume that a family history of breast cancer rules out MHT entirely. This is not the current position.

A family history of breast cancer is a reason for a more careful conversation. This is particularly true if there is a confirmed BRCA1 or BRCA2 mutation, or multiple first-degree relatives diagnosed at young ages. In these cases, MHT decisions are best made with input from a menopause specialist, sometimes alongside a genetic counsellor or breast specialist.

But a single family member with breast cancer, or a family history without confirmed genetic risk, does not automatically mean MHT is off the table. Both the Australasian Menopause Society and the International Menopause Society support an individualised approach in these cases, weighing symptom severity, personal risk profile, and the specific family pattern [9,13]. The conversation is individual, not a blanket no.

What about a personal history of breast cancer?

This is a different conversation to family history.

A family history of breast cancer means an increased risk profile, but the woman herself has not had cancer. A personal history of breast cancer means the woman has been diagnosed and treated. The evidence base, the conversation with her oncology team, and the considerations are all different.

For women with a personal history of breast cancer, systemic MHT (oestrogen taken by patch, gel, spray, or tablet) has traditionally been a no. For decades, it was treated as a clear contraindication. That position is now being actively reconsidered.

A 2025 multidisciplinary consensus statement published in Menopause, the journal of the North American Menopause Society, brought together GP menopause specialists, gynaecologists, medical oncologists, breast surgical oncologists and patient representatives (including Dr Louise Newson, a leading UK menopause specialist) to review the evidence on MHT after breast cancer. The panel concluded that some women may choose to take MHT off-label, accepting an increased risk of relapse in exchange for relief from menopausal symptoms and improved quality of life. The decision belongs to the individual woman, made with her oncology team [14].

Dr Avrum Bluming has argued the same position in greater depth, in a 2022 paper in The Cancer Journal titled "Hormone Replacement Therapy After Breast Cancer: It Is Time," reviewing 25 studies of MHT after breast cancer published between 1980 and 2013 [15].

This is a position-shift, not a settled answer. The standard Australian clinical position has not yet moved. But the international conversation has opened up considerably, and it is no longer a simple no for women in this situation. For some women, with their oncology team, the conversation can now be had.

What about local vaginal oestrogen for breast cancer survivors?

Vaginal dryness, painful sex, and recurrent urinary tract infections after menopause, known collectively as genitourinary syndrome of menopause (GSM), can severely affect quality of life. Low-dose vaginal oestrogen, applied locally, has minimal absorption into the rest of the body.

For women with a personal history of breast cancer, local vaginal oestrogen may still be an option in consultation with the oncology team. The Australasian Menopause Society and international consensus statements support this as an individualised consideration [9,16]. This should be a conversation, not an automatic no.

What about regular breast screening?

Whether you are considering MHT or not, once you are 50, regular breast screening matters.

In Australia, the BreastScreen Australia program offers free mammograms every two years for women aged 50 to 74. Women aged 40 to 49 and 75 and over are also eligible for free screening, though they are not actively invited [17]. Screening can be booked through BreastScreen in your state or territory.

All women in midlife should be aware of any new lump, skin change, nipple discharge, or change in breast feel or appearance. Self-awareness sits alongside formal screening, not instead of it.

[PLACEHOLDER] A free Breast Self-Check Guide will be available at menopausehub.com.au/links (when published).

If you notice anything that concerns you between scheduled screens, do not wait for the next one. See your GP.

What does this mean for you?

Whether or not MHT is right for you is an individual decision. It depends on your symptoms, your personal and family history, your other health conditions, and what matters to you about quality of life.

What it does not depend on is information from 2002.

If you have been told MHT is too risky because of breast cancer, the conversation deserves a closer look. The hormones now used in Australia are different to those tested in WHI. The breast cancer signal looks different on long-term follow-up. The role of progestogen type is now better understood. The picture for women without a uterus is different again. And the evidence on related cancers, including endometrial and bowel, is part of the picture too.

You have the right to a current conversation, especially if you are experiencing symptoms that affect your daily life. MHT, like all medication, has benefits and risks. The benefits can be substantial. The risks are individual. The decision is yours, in conversation with a GP who keeps up with current menopause evidence and guidelines.

I will never tell anyone what to decide.

What I aim to do is help women know the real numbers and the current context, so we can have a proper discussion, and so I can answer questions based on current information. I help women talk through the risks and the fear they may have, and how those might apply to them. And I help them work out what to ask their GP, so they can get information about their individual risk if MHT is something they want to consider, or want to know more about.

That is the conversation worth having.

In simple terms

- The current evidence shows MHT and breast cancer is a small, specific risk that depends on the type of MHT, the type of progestogen, and your individual risk profile.

- Oestrogen-only MHT (for women without a uterus) does not increase breast cancer risk and may decrease it. WHI's own data show 23% lower breast cancer development and 40% lower breast cancer death.

- Combined MHT (for women with a uterus) carries a small additional breast cancer risk in absolute terms. Comparable to lifestyle risks like alcohol or excess weight that women rarely worry about.

- The type of progestogen matters. Body-identical micronised progesterone (Prometrium) shows roughly a third less breast cancer risk than older synthetic progestins.

- Combined MHT may also reduce endometrial cancer risk and is associated with reduced colorectal cancer risk.

- A family history of breast cancer means a more careful, individualised conversation. Not an automatic no.

- A personal history of breast cancer is a different conversation, and the position is now being actively reconsidered with new consensus statements supporting individual choice in collaboration with the oncology team.

- Whether you are considering MHT or not, once you are 50, regular breast screening matters. BreastScreen Australia offers free mammograms every two years for women aged 50 to 74.

Want the complete picture?

There are three free resources to take this further.

[PLACEHOLDER] Breast Self-Check Guide. A one-page guide on what to look for, when to screen, and when to see your GP. menopausehub.com.au/links (when published).

[PLACEHOLDER] MHT Complete Guide. The full plain-language guide. menopausehub.com.au/links (when published).

Recommended external resource: British Menopause Society infographic, Understanding the Risks of Breast Cancer, available free at thebms.org.uk. A clear visual comparison of MHT-associated breast cancer risk alongside common lifestyle risks.

Next in the series

The next blog walks through the words that get used around hormone therapy. Body-identical, bioidentical, synthetic, compounded. Four words that sound similar and mean very different things. If you have been told you should be on bioidentical hormones, or have been quoted hundreds of dollars for a compounded preparation, the next blog is for you.

[Link to Blog 4: Body-Identical, Synthetic, Bioidentical, Compounded. What These Words Mean. To be added when blog 4 is published.]

This information is educational only and does not constitute personal medical advice. Always consult a qualified health professional about your individual circumstances.

© 2026 Menopause Hub | Anna Pattison | Former Registered Nurse, Clinical Myotherapist, Menopause Mentor | menopausehub.com.au

CITATIONS

[1] Rossouw, J.E., et al. (2002). Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women's Health Initiative randomized controlled trial. JAMA, 288(3), 321-333.

[2] Manson, J.E., et al. (2013). Menopausal hormone therapy and health outcomes during the intervention and extended poststopping phases of the Women's Health Initiative randomized trials. JAMA, 310(13), 1353-1368.

[3] Anderson, G.L., et al. (2012). Conjugated equine oestrogen and breast cancer incidence and mortality in postmenopausal women with hysterectomy: extended follow-up of the WHI randomised placebo-controlled trial. Lancet Oncology, 13(5), 476-486.

[4] Fillon, M. (2024). The association between menopausal hormone therapy and breast cancer remains unsettled. CA: A Cancer Journal for Clinicians, 74(3), 217-222. Quote attributed to Dr Avrum Z. Bluming, MD.

[5] Australasian Menopause Society. Information Sheet — MHT and Breast Cancer Risk. menopause.org.au

[6] British Menopause Society. Understanding the Risks of Breast Cancer infographic. thebms.org.uk

[7] Asi, N., et al. (2016). Progesterone vs. synthetic progestins and the risk of breast cancer: a systematic review and meta-analysis. Systematic Reviews, 5(1), 121.

[8] Fournier, A., et al. (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.

[9] Australasian Menopause Society. Position Statement on Menopausal Hormone Therapy. menopause.org.au

[10] Tempfer, C.B., et al. (2020). Menopausal Hormone Therapy and Risk of Endometrial Cancer: A Systematic Review. Cancers, 12(8), 2195.

[11] Simin, J., et al. (2017). Menopausal hormone therapy and cancer risk: An overestimated risk? European Journal of Cancer, 84, 60-68.

[12] Menopause Alliance Australia. MHT and Gynaecological Cancer information sheet. menopausealliance.au

[13] International Menopause Society. (2016). Global Consensus Recommendations on Menopausal Hormone Therapy. IMS Position Statement.

[14] Glynne, S., Simon, J., Branson, A., Newson, L., et al. (2025). Menopausal hormone therapy for breast cancer patients: what is the current evidence? Menopause. Multidisciplinary consensus statement.

[15] Bluming, A.Z. (2022). Hormone Replacement Therapy After Breast Cancer: It Is Time. The Cancer Journal, 28(3), 183-190.

[16] The North American Menopause Society. (2020). The 2020 genitourinary syndrome of menopause position statement. Menopause, 27(9), 976-992.

[17] BreastScreen Australia. Department of Health and Aged Care. health.gov.au/our-work/breastscreen-australia-program

[18] Davis, S.R., Magraith, K. (2023). Practitioner's Toolkit for the Management of the Menopause. Medical Journal of Australia.