For more than 20 years, one fear has shaped how many women think about HRT: breast cancer.
It's understandable. In 2002, early results from the Women's Health Initiative trial made headlines around the world, and HRT use fell dramatically almost overnight. Many women who were struggling stopped treatment, and many more never started.
This Breast Cancer Awareness Month, we want to set out what the evidence shows today: honestly, in real numbers, and without either scaremongering or dismissing a genuine concern.
The biggest analysis
In 2019, The Lancet published the largest analysis ever done on HRT and breast cancer, by the Collaborative Group on Hormonal Factors in Breast Cancer. It brought together data from studies around the world, including more than 108,000 women who developed breast cancer.
It found that most types of HRT were linked to a small increase in breast cancer risk, that the risk grew the longer HRT was used, and that it was higher for combined HRT (oestrogen plus progestogen) than for oestrogen alone.
What that means in real numbers
Relative risks can sound frightening, so here are the absolute numbers the researchers estimated for women of average weight starting HRT at 50 and taking it for five years. Each figure is the chance of developing breast cancer between the ages of 50 and 69.
Never used HRT: about 63 in every 1,000 women.
Oestrogen-only HRT: about 68 in every 1,000, or one extra case for every 200 women.
Oestrogen plus progestogen taken some days of the month: about 77 in every 1,000, or one extra case for every 70 women.
Oestrogen plus progestogen taken every day: about 83 in every 1,000, or one extra case for every 50 women.
For ten years of use, the extra risk was roughly double. Some extra risk persisted for years after stopping, depending on how long HRT had been used.
Some important reassurance
Vaginal oestrogen (low-dose creams, pessaries or rings for dryness and urinary symptoms) was not linked to an increased risk of breast cancer.
Short-term use of less than a year carried little risk.
The picture for oestrogen alone is mixed in a reassuring direction. In the Women's Health Initiative randomised trial, women who had had a hysterectomy and took oestrogen alone actually had fewer breast cancers and fewer breast cancer deaths than women on placebo, over about 20 years of follow-up. Combined HRT in that trial was linked to more breast cancer diagnoses, but not to more breast cancer deaths.
The Lancet analysis and the WHI trial don't fully agree, especially on oestrogen alone. That's partly because they used different types of study and different preparations. It's one reason expert menopause societies emphasise looking at the whole picture rather than a single number.
Weighing it up
Breast cancer risk is real and worth taking seriously. But it isn't the only thing on the scales. Major menopause societies, including the British Menopause Society and the International Menopause Society, have stressed that it should be considered alongside HRT's benefits: relief from symptoms, better quality of life, and protection of bone health.
It's also worth knowing that other everyday factors affect breast cancer risk too, including alcohol, physical activity and weight after menopause. Every woman's starting point is different, depending on her age, family history, personal history and type of HRT.
That's why there's no single right answer. There's only the right decision for you, made with good information.
Questions to ask your GP
What is my own baseline risk of breast cancer, given my family and personal history?
Which type of HRT, and which progestogen, would you recommend for me, and why?
How long should I plan to take it, and how often should we review it?
Would vaginal oestrogen alone be enough for my symptoms?
Be breast aware, whatever you decide
Get to know how your breasts normally look and feel, and see your GP promptly about any changes, such as a lump, a change in shape or skin, or nipple changes. In Ireland, BreastCheck offers free mammograms to women aged 50 to 69. Please take up your invitation.
Fear has made this decision for too many women, for too long. Our hope is that the facts help you make it for yourself.
Always with balance. Always with you.
This article is general information, not personal medical advice. If you have had breast cancer, or have a strong family history, please talk to your specialist team about your options.
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Blog by Georgie Sliney McCormack & Helen Flynn
Georgie and Helen are the co-founders of The Balance Project. Through their work, they are committed to making women's health information more accessible, informed, and empowering. They believe better conversations lead to better understanding, better support, and better outcomes for women.
