She was 52, two years into HRT, when the letter came: her routine mammogram needed a second look. A week of not sleeping, then more images, then the all-clear. The radiologist mentioned, almost in passing, that her breasts were "quite dense" and that HRT can do that.
Nobody had told her either thing before. She did not know her breasts were dense, did not know it mattered, and did not know her HRT could change what a mammogram shows.
Breast screening is one of the most important appointments of midlife, and most women go into it knowing very little about how it works. If you take HRT, there are a few things worth understanding.
Across the UK, women in their fifties and sixties are invited for a mammogram roughly every three years. In England the programme runs from 50 up to the 71st birthday, and women older than that can still ask to be screened.
A mammogram is a low-dose X-ray of each breast. Fatty tissue looks dark on the image. Glandular and fibrous tissue, the dense part, looks white. Cancers also look white.
That is the problem density creates.
Breast density describes how much of the breast is glandular and fibrous tissue compared with fat. It is not about size or firmness; you cannot tell by feel. It is seen only on a mammogram.
Dense breasts matter for two reasons.
Cancers are harder to see. A small white tumour against a white background is easily missed, a little like looking for a snowball in a snowstorm.
Density is itself a risk factor. According to the BRAID research team, around one in ten women have very dense breasts, and between 50 and 70 those women have up to four times the breast cancer risk of women with very low density.
Density usually falls with age, especially after menopause, as glandular tissue is replaced by fat. Most women in the UK are not routinely told their density after a mammogram.
Oestrogen stimulates breast tissue, and some women taking HRT, particularly combined HRT containing a progestogen, develop denser breasts.
The clearest evidence comes from the Women's Health Initiative trial of combined HRT. After one year, 9.4 per cent of women taking hormones had an abnormal mammogram, compared with 5.4 per cent of those taking placebo. Cancers that were diagnosed in the hormone group tended to be slightly larger and more often at a later stage, which the authors linked partly to the effect of hormones on mammograms.
That trial used an older oral combination that is less commonly prescribed in the UK today, and it does not mean every woman on HRT will be affected. But it shows two things worth knowing: HRT can increase the chance of a recall for more tests, and it can make mammograms a little harder to read.
For the separate question of whether HRT raises the risk of breast cancer itself, and by how much, see the truth about HRT research. The type of progestogen may matter, as we explain in choosing the progestogen in your HRT.
The most important recent study on density came from the UK. The BRAID trial, published in the Lancet in 2025, included more than 9,000 women with dense breasts whose standard mammograms had been normal. They were offered an extra scan.
Per 1,000 women screened, the extra scans found:
For comparison, standard mammography finds about 8 cancers per 1,000 women in this group. In other words, the best additional scans found more than twice as many cancers again, all of which the standard mammogram had missed. The researchers estimated that offering these scans to women with dense breasts could find thousands of extra cancers a year in the UK.
This is not yet part of routine NHS screening, and supplemental scans have their own downsides, including more recalls and more biopsies that turn out to be benign. But it is the strongest evidence so far that density matters, and policy may change.
Go to your screening appointments. Whatever its limits, regular screening finds cancers earlier than waiting for symptoms.
Tell the radiographer you are on HRT. It is useful information for whoever reads your images.
Ask about your breast density. If you have had a recall or been told your breasts are dense, it is reasonable to ask what that means for you.
Do not stop HRT before a routine mammogram unless a clinician specifically advises it. There is no standard UK advice to do so.
Know your normal, and report changes. Screening every three years leaves long gaps. Cancers that appear between screens, called interval cancers, are more common in dense breasts. Get to know how your breasts look and feel, and see your GP promptly about:
Tell your GP about family history. If close relatives have had breast or ovarian cancer, especially at a young age, you may qualify for earlier or more frequent screening.
Being called back after a mammogram is frightening, and most recalls do not turn out to be cancer. They usually mean an area needs a closer look with more images or an ultrasound. Women on HRT and women with dense breasts are more likely to be recalled. A recall is a reason to attend quickly, not a diagnosis.
For breast symptoms that come and go with hormone changes, see breast tenderness and hormones.
Does HRT make breasts denser?
In some women, yes, particularly combined HRT. In the Women's Health Initiative trial, more women on combined HRT had abnormal mammograms than on placebo, partly because of changes in breast tissue.
Why does breast density matter?
Dense tissue and cancers both appear white on a mammogram, so cancers can be harder to see. Very dense breasts are also linked to a higher risk of breast cancer.
How do I find out if I have dense breasts?
Only a mammogram can show it. Most women in the UK are not routinely told, but you can ask, particularly after a recall.
Should I stop HRT before my mammogram?
There is no standard UK advice to do this. Keep taking it unless a clinician specifically advises otherwise, and tell the radiographer you are on HRT.
What did the BRAID trial show?
In over 9,000 women with dense breasts and a normal mammogram, extra scans found up to 19 additional cancers per 1,000 women. It is not yet part of routine NHS screening.
Can I be screened after 71?
In England, women over 71 are no longer invited automatically but can ask to be screened every three years.
Sources: Chlebowski RT et al., Influence of estrogen plus progestin on breast cancer and mammography in healthy postmenopausal women: the Women's Health Initiative randomized trial, JAMA 2003;289(24):3243-53 · Gilbert FJ et al., Comparison of supplemental breast cancer imaging techniques: interim results from the BRAID randomised controlled trial, Lancet 2025 · NHS breast screening programme information · Educational only, not medical advice. See your GP promptly about any breast change.
Keep reading: The truth about HRT research · Choosing the progestogen in your HRT · Breast tenderness and hormones · HRT side effects · HRT benefits · Take the free Hormone Quiz