Why an all-clear mammogram can be wrong – and the life-saving question to ask

Telegraph

16-05-2025

When Sarah Fleetwood found a lump in her right breast on the day of the King's Coronation, May 2023, she knew she needed to get it checked. It was the third lump over the past few years. In 2017 it had proved harmless, and in 2021 she'd been told 'you just have lumpy boobs'. But now a third mammogram was looming.
When this latest mammogram proved inconclusive, the Berkshire mother of two was then sent for an ultrasound, which had shown 'an unusual mass which needed further investigation,' says Fleetwood. 'So then they took a biopsy.'
Unfortunately, the cancer had already spread to her lymph nodes and was stage three – so in July 2023 Fleetwood underwent a mastectomy and lymph node removal and began a course of aggressive chemotherapy.
At no point was Fleetwood ever informed of her breast density and how this can make it hard to spot cancer on a mammogram. 'The evidence suggests it's highly likely that the cancer had been growing in my right breast for many years. Had I asked for an ultrasound after my second mammogram in 2021 – the cancer might have been detected sooner, I may not have needed such aggressive chemo and years of hormone treatment,' says Fleetwood. 'Women need to be clued up about this.'
'After the second mammogram I'd always felt niggling doubt, I wanted to ask 'are you sure?' when I was told 'everything is fine'. Because I knew they weren't able to see anything from the first one I'd had, so how would they know with this one?'
While grateful for the care she received, Fleetwood believes that more awareness of dense breasts, and their link to an increased risk of cancer, could have resulted in a different outcome for her. Early intervention may have saved her from having her whole breast removed.
Fleetwood is far from alone in not knowing what her own breast density is. A new survey of 2,000 UK women aged over 18, found that 93 per cent of women in the UK are unaware of what dense breast means.
Moreover, 83 per cent of women surveyed didn't realise that a clear mammogram result doesn't always mean they are cancer-free.
What does having a dense breast actually mean?
'Breast density is a mammographic measurement of how much fibroglandular tissue there is in a woman's breast versus fatty tissue,' says Harleen Deol, a consultant oncoplastic breast surgeon for East and North Herts NHS Trust, and a specialist breast cancer advisor to Genesis Care.
Approximately half of all women aged 40 or above who have a mammogram have dense breasts. 'A mammogram might not show up a tumour on someone with dense breasts,' adds Deol.
Breast tissue, she explains, is composed of three types of tissue: fibrous connective tissue, glandular tissue and fat.
'The more fibroglandular tissue, the denser the breast. The denser the breast, the more challenging it is to identify a tumour in a mammogram, because cancers show up the same colour (white) as the dense breast tissue, making it difficult to differentiate between the two. You can't tell whether you have dense breasts by self-examination, or an ultrasound or an MRI. The dense breast tissue grading is only on a screening mammogram set by the Royal College of Radiologists in the UK.'
There are four categories of breast density, according to Deol.
Class A: This means your breast is made up of lovely, beautiful, entirely fatty breast tissue, meaning we can clearly see through the whole of the breast in a mammogram. About 10 per cent of women are blessed with fatty breasts.
Class B: It is when you have little scattered areas of this fibroglandular tissue, so we can mostly see through it on a mammogram. Around 40 per cent of women are in category B.
Class C: A further 40 per cent fall into this category, meaning there are multiple areas, like little islands of very dense breast tissue scattered across the breast within a background of otherwise fatty tissue.
Class D: The remaining 10 per cent of women fall into this category. These are extremely dense breasts, with dense fibroglandular tissue and minimal or no fat.
Why knowing your breast density is crucial
For women with very dense breasts (category D) there is up to a six times higher risk of developing breast cancer. 'And not just because there is a difficulty in detecting cancer in dense breasts – but with factors due to the nature of very dense breast tissue itself,' says Deol.
As of January in United States, all women receiving a mammogram will now be informed about their breast density. Here in the UK, however, this is not standard practice.
'There is no way that the NHS can cope at the moment with telling women their breast density, because then women [with dense breasts] would naturally want to ask what else can be done to reduce their risk of them developing breast cancer and the resources are not available for breast screening with MRI scans,' says Doel.
'The truth is that ideally all patients with dense breasts would be sent for further investigation after their mammograms – either an ultrasound, followed by a biopsy if necessary, or an MRI,' Doel continues. 'The NHS couldn't cope with that number of MRI scans, they'd have to buy thousands more machines and hire more staff as standard MRIs take 45 minutes to perform.'
Alongside her NHS work, Deol works as a specialist advisor for GenesisCare, a private healthcare provider who are the first in the UK to inform all patients who undergo a mammogram of their breast density as standard practice. Their new campaign 'Keep Abreast of Your Breast Density' sets out to educate women about the risks of dense breasts. They also have launched a new breast screening service where patients who have dense breast tissue can pay for a rapid MRI scan (£450) for early detection of cancer.
Private MRI breast scans are available across the UK starting from £350 per breast, and the standard MRIs take 45 minutes, while the rapid breast MRI screening ones only take 15 minutes and screens both breasts. Some latest studies have also revealed that the rapid test can be just as effective as the longer one.
Private hospitals as well as the NHS offer full breast MRIs for women who have a medical need. For example, a breast cancer not seen clearly on a mammogram, but these have to be medically indicated and ordered by a doctor. The benefit of a rapid screening MRI is that patients can self-refer if they are paying themselves, or be referred by the breast surgeon. The rapid MRI takes only 15 minutes rather than 45 minutes as it is specifically designed to be used for breast screening, not for women who have breast symptoms or a lump. (They should see a breast surgeon first).
Deol recommends a private MRI – if women can afford it – she insists she's 'not trying to give it a hard sell' or advertising on their behalf. 'My life's mission is empowering women to have the knowledge to self advocate, to be able to look after their own health, so they can get a quicker diagnosis and we can save more lives,' she says.
Yet women with dense breasts shouldn't panic. A 2015 study of 365,000 women aged 40 to 74 in the Annals of Internal Medicine showed that not all women with dense breasts are at a higher risk of breast cancer. Only when other risk factors, such as age, ethnicity and family history of breast cancer, were added to the equation did tissue density correlate with increased risk of breast cancer after a clear mammogram result.
Who is most at risk of dense breasts?
Breast size is not a factor as anyone can have dense breasts, but women with a very low BMI are likely to have more dense breasts.
'Breast density reduces as we age, but can be increased while hormone replacement therapy [HRT] is used during the menopausal years,' says Deol. 'Dense breast tissue is present in over half of the women having mammograms over the age of 40 and although breast size is not a factor relating to dense breasts, women with a very low BMI are more likely to have dense breasts as they have a lower fat content in the breasts.
It's also been found that people from Asian or Afro-Caribbean descent are more likely to have dense breast tissue but it can also run in families.
'Unfortunately, for women – including myself – who've never had children or breastfed there is an increased risk of dense breasts. HRT use might also increase the risk, because breasts love oestrogen, and oestrogen causes the breasts to remain more youthful – and more dense.'
(Deol doesn't want to put women off using HRT however, and still uses it herself: 'It's a balancing act of risks versus quality of life.')
Why can't I just be treated on the NHS?
You can, Deol reassures us. The last thing women should do is panic. 'If you have any symptoms, such as a lump, puckering [also known as dimpling] or any significant change on your breasts then of course go to your GP and you will be referred and looked after in a timely manner with the NHS. Around half of women over 40 have dense breasts, but we do not know what percentage will get breast cancer.
Under the NHS screening programme, women aged between 50 and 70 are invited to attend a mammogram every three years.
Women under the age of 40 do tend to have more dense breast tissue, which is normal at that age. As we grow older, breast density tends to reduce overall, but remains very dense in 10 per cent of women. Every time we X-ray any part of the body we have to be certain of the benefit and that is not clear in women under the age of 40.
If a woman is having a routine NHS breast screening mammogram (ie they have no symptoms/lumps) then any abnormality shown on a mammogram will be checked with an ultrasound scan, and in some hospitals, a 3D mammogram (tomosynthesis) to see if the abnormality is visible and then to have a biopsy.
'The NHS screening programme is fantastic, so please do go when you are invited for a mammogram. I recommend all women to have regular screening mammograms as these still provide a lot of information and detect breast cancers early in most women. Self-examination monthly is also vital for all women of all ages.'
How to find out about your breast density grading
A further precaution which Deol advises, is for women to proactively find out about their breast density by writing and asking for it. (You can't just ask the radiographer who carries out the procedure on the day, Deol explains, as the images have to be sent to Consultant Radiologists to then be reported later. )
'When women receive their mammogram report letter from the NHS Breast Screening Programme, there are contact details for the unit that reported their mammogram – they can use this address to request their breast density grading,' says Deol. 'Similarly, they can request their density from any hospital where they have a mammogram.'
'The NHS Breast Screening Programme does not currently offer MRI scans of the breasts for any woman routinely, but it does offer MRI scans at symptomatic breast clinics, usually where cancer is diagnosed but cannot be seen on a mammogram,' explains Deol.
And women shouldn't fear not being able to access the NHS for treatment after undergoing a private test.
'If a private MRI shows a cancer or a suspicious lesion then of course patients can be treated on the NHS,' reassures Deol. 'They would just need the MRI report for their GP to refer them to their local NHS Breast Clinic'
The best way for women to look after their breasts
Then if money were no object, suggests Deol, that from the age of 40 (10 years before they become eligible for the NHS programme) women seeking reassurance might wish to consider finding a local clinic to have a private screening mammogram every two years. Costs range from between £200-400 for a standard mammogram.
At the time of the mammogram, a patient should specifically enquire about their breast density category. If they learn they have dense breasts, Deol recommends a private rapid MRI. Then they should continue having a mammogram every two years, and if they have dense breasts, she advises a rapid MRI around the same time. As there's no radiation with an MRI, says Deol, they could consider going every year, if they could afford it and wanted peace of mind.
'We know so much more about breast cancer and the survival rates are so much better than ever before' says Deol. 'The new research showed us that 75 per cent of women would feel more confident in managing their breast health if they had clearer information about breast density after a mammogram.
'It is important to know that breast cancer patients who have dense breasts are no more likely to die from breast cancer than cancer patients with fatty breasts, but early detection vital for the best treatment of breast cancer, so, please do ask the question – it could save your life'