Susan Leeson thought her clear mammogram meant she could briefly relax about her risk of breast cancer until her next routine screening in three years’ time.
’I thought great, one less thing to worry about for a bit,’ she says.
Susan, 56, who is married to a corporate lawyer and has a teenage daughter, now desperately wishes she hadn’t put so much faith in the result. For seven months later, and only after going to A&E with agonising back pain, Susan discovered she had a fractured spine.
And the cause? Cancer that had spread from a strawberry-sized tumour growing in her right breast, to her ribs, hip and three different parts of her spine. In total, it was in eight different spots around her body and it was incurable.
’In the split second that I found that out, my whole world changed for good,’ says Susan, a former career coach who lives in Balham, South-West London. 'I was in deep shock and I just kept saying over and over 'but I recently had a clear mammogram’.
I was very emotional, but I had to try to pull myself together enough to go home and break the news to my daughter, who was only 15 at the time.’
Had her cancer been spotted on the mammogram, she says: 'The chances are that I would have had a little operation and be getting on with life.’
Instead, Susan has been told she has possibly only two years left – and she is now channelling the anger and frustration she feels at her situation into helping others. 'I want other women to know that there’s a whole bunch of cancers that get missed by mammograms,’ she says.
Susan Leeson, 56, thought her clear mammogram meant she could briefly relax about her risk of breast cancer until her next routine screening in three years’ time
Tragically, this is true – for although mammograms do help spot cancers, they aren’t failsafe. Every year more than 1,000 women given the all-clear, actually have the disease.
Women are offered a mammogram – two X-rays of the top and two of the side of each breast – every three years, starting from when they are aged 50 to 53 and extending until 70.
The aim is to find cancers when they are too small to see or feel, and are easier to treat.
Almost 20,000 cancers were detected in the 2.18 million women in England who had a routine mammogram in 2022-2023.
But each year thousands of women are also diagnosed with 'interval cancers’ – breast tumours that are diagnosed within three years of a clear mammogram and before the next routine screening is due.
Around 6,000 women are found to have interval cancers each year in England, according to Public Health England, 80 per cent had 'no cancer visible’ during their last mammogram but, in 20 per cent of cases (1,200 women), there was a cancer 'which was not picked up’. This is because the visible changes that might indicate cancer were 'subtle’ or they were simply missed, according to Public Health England.
How is it that technology theoretically so precise that it can detect abnormalities as small as a 1-2mm – not much bigger than a pinhead – missed these cancers?
Indeed, mammograms can detect not just tiny cancers, but also tiny specks of calcium, known as calcifications, which can be benign but may also be a 'sign of pre-cancerous changes in the breast,’ says Caroline Rubin, a consultant radiologist specialising in breast imaging at University Hospital Southampton.
The difficulty is that abnormalities may be 'really subtle – known as distortions, small, well-defined masses, or micro-calcifications which are no bigger than a speck’, she says.
With interval cancers, in some cases there may be no visible sign on the mammogram. If, for example, a cancer is in the far edge of the breast it may be out of shot – a rare occurrence but one that can happen, says Dr Rubin.
The type of breast tissue is also relevant: around 40 per cent of women have dense breasts and this thicker tissue makes it harder to spot cancer. Fat tissue looks black on a mammogram and abnormalities look white, but dense breast tissue also looks white 'so in that case we are looking for a white mass in a white background’, says Dr Rubin.
’A significant number’ of breast cancers missed on mammogram are due to the breast density, adds Professor Kefah Mokbel, a consultant breast surgeon at the London Breast Institute, who has been involved in research into new types of screening.
Almost 20,000 cancers were detected in the 2.18 million women in England who had a routine mammogram in 2022-2023
In some countries, if a mammogram reveals dense breast tissue the woman is routinely also given an ultrasound (which can spot tumours in dense breasts) – 'but this is not the case in the NHS’, he says.
This was ruled out following a review in 2019 which determined that it would lead to more false positive results and unnecessary biopsies.
The NHS does not even routinely let women know even if a mammogram reveals they have dense breasts – which he argues is wrong 'as not only do the dense breasts make it harder to spot any tumour, they can also increase the risk of cancer’.
This is possibly because there are more cells in them that have the potential to mutate.
’In some states in the US, it is illegal not to inform a woman if a mammogram shows she has dense breasts,’ says Professor Mokbel. Not telling women they have dense breasts, he says, denies them 'the opportunity to take steps to reduce their risk of breast cancer – for example, following a healthy diet, avoiding ultra-processed food, taking vitamin D supplements and eating antioxidant-rich foods’.
Susan later found out she had 'mixed density breasts’ although, in her case, human error may have played a part.
When her original mammogram was reviewed after her diagnosis, seven out of the ten reviewers (from the hospital where she’d had the mammogram, St George’s in Tooting, and from four other hospitals) said they would have recalled her for more checks such as an ultrasound. Some commented that a 14mm 'mass’ was visible.
The apparently clear results of the mammogram were especially significant for Susan because, then aged 53, she was about to undergo a hysterectomy as she had a fibroid (a benign growth) the 'size of melon’ pressing on her bladder.
The surgery would immediately bring on the menopause and it was suggested she have HRT implants, placed under the skin during the operation, to avoid being thrown straight into menopause while recovering from major surgery.
The implants would release hormones for six months, which carried 'a slightly increased risk of breast cancer’, Susan says – which is why she asked to have the mammogram she was due anyway, 'to be on the safe side, and if that was clear then I could have the HRT’.
When the mammogram came back clear in May 2021, Susan pushed ahead with the hysterectomy that September. Then, in January 2022, she collapsed at home with crippling backache and had to call an ambulance. Doctors in A&E told Susan the pain was due to two bulging discs and 'lesions’ on her spine that they initially attributed to the bone- thinning condition, osteoporosis.
’I was told I just needed painkillers and rest,’ says Susan. She was called back for more scans, but a month later hadn’t had the result so paid privately for a doctor to review them.
At that appointment, on February 9 2022, the true cause was revealed.
’Cancer was dotted around so much of my body that the doctor said on the scan it looked as if someone had flicked a wet paintbrush at me,’ says Susan. 'I woke up the next day in tears and the only way I could get through the first few months was by nibbling on diazepam [a tranquiliser] that I’d previously been given for the back pain.
’The first thing my oncologist said is that the HRT had accelerated the cancer. It might have been sitting there for years not growing much – since I was diagnosed, it hasn’t grown – but the HRT was like pouring fuel on the fire.’
Susan, who is married to a corporate lawyer and has a teenage daughter, now desperately wishes she hadn’t put so much faith in the result of the mammogram
There are guidelines in place to try to avoid the risk of human error around checking mammograms – for example, all mammograms must be examined by two readers – either radiographers (who study radiography and then specialise in mammograms) or radiologists (specialist doctors trained in radiology). They have to scrutinise at least 5,000 mammograms a year to maintain their experience.
But it is fast-paced work – according to a study in the European Journal of Radiology in August, in the NHS around a minute (give or take 27 seconds) is spent checking a mammogram.
And as Susan points out, there is no extra guidance about analysing the mammograms of women with dense breasts – 'even though it’s acknowledged that they make it harder to spot cancer’.
The number of women recalled for further checks (normally another mammogram, an ultrasound or a biopsy) is reviewed to ensure the readers stick within 'achievable’ or 'acceptable’ levels.
According to the most recent NHS breast screening standards, 'acceptable’ is recalling less than 9 per cent of those having their first screening mammogram and less than 4 per cent for those having subsequent mammograms.
’Achievable’ is recalling less than 7 per cent of their first and less than 3 per cent having subsequent mammograms – NHS England says that the achievable rate is an 'aspirational’ target.
A spokesperson told Good Health: 'The vast majority of units are within the acceptable level and rates are regularly reviewed within screening units as well as by commissioning and quality assurance teams.’
Indeed 6.2 per cent of women having their first mammogram and 2.8 per cent of those having subsequent mammograms were recalled, according to NHS Digital figures for 2022/23.
In a written answer to a question from Susan’s MP about the number of recalls last month Andrew Gwynne, under-secretary of state for public health and prevention said that NHS England would have 'a full review of all standards in screening year 2025/26 and this would determine whether the acceptable and achievable limits should be changed’.
The dilemma is that increasing the rates of women being recalled may increase false positives.
In the past year, more than 72,000 women offered screening were sent for further checks and 74 per cent were found not to have cancer. This can mean unwarranted tests, not to mention needless anxiety.
But given the choice, understandably, Susan says: 'I would rather have a few weeks’ anxiety than to be living with advanced cancer. If I’d known what I know now I would have paid to go privately to have a mammogram and an ultrasound.’
A spokesperson for St George’s University Hospitals NHS Foundation Trust said: 'We understand how distressing this diagnosis must be for Mrs Leeson and her family, and are very sorry her cancer was not picked up at screening and that she is unhappy with her care.
While all mammograms are assessed by at least two qualified clinicians, screening tests are unfortunately not 100 per cent accurate – but we always review cases where a patient’s cancer is diagnosed between routine screening appointments to see if there is anything we could have done differently.’
Dr Rubin believes that one simple way to reduce interval cancers is to reduce the interval between mammograms.
’Three years is a long time and the numbers of interval cancers that occur increases over that time,’ she says. 'Other countries have a two-year programme and changing this here has been discussed on and off for years.’
This may help those interval cancers caused by fast-growing cancers – which grow in between screenings.
’While a grade 1 [usually the slowest growing] can stay in the breast for years without a change; a grade 2 can double in size in six to 12 months; and a grade 3 can do that in two to three months,’ says Professor Mokbel.
The current breast cancer screening programme is 'very good’ at detecting grade 1 and grade 2 invasive breast cancers, which make up the vast majority of cases, says Dr Roger Blanks, an epidemiologist at the University of Oxford, who has been involved in cancer screening research.
However, he says, grade 3 cancers 'are not easily detected using the current technology and these often occur as interval cancers’.
Indeed, Dr Rubin adds: 'Grade 3 [tumours] can look quite benign or hide in breast tissue.’
Dr Blanks thinks changing the recall rate is unnecessary, 'rather it is likely that an evolution in screening technology is required’.
Advances are under way. The NHS has started using 3D mammography, or tomosynthesis, during which the X-ray moves around the breast, taking images at different angles, providing a more detailed 3D image of the breast.
Currently this is only offered to women who have been recalled.
Another study, being carried out at multiple sites across England, is looking at 'fast MRI’, which takes fewer images – and so takes three minutes, not 20 minutes as traditional MRIs do.
Traditional MRIs can spot tumours even in dense breasts and it’s already known that fast MRI can do so, too – the new trial is testing the technology on average density breasts.
Artificial intelligence (AI) may also improve the accuracy of breast screening.
In a 2020 study more than 170,000 mammogram results from the UK, South Korea and the US – and their subsequent outcomes – were also analysed by AI.
Writing in the Lancet, researchers said AI produced a 'significant improvement in radiologists’ performance’ as a diagnostic tool.
Cancer charities meanwhile, are keen to emphasise the need for women to check their breasts.
Recent research by Breast Cancer Now found that 44 per cent of women in the UK don’t check their breasts regularly, something Sally Kum, the charity’s associate director of nursing, healthcare professional engagement and health information, describes as 'deeply concerning’.
Susan’s cancer, however, could not be felt, even when she was diagnosed. She is now on capecitabine, a chemotherapy tablet, which she takes for seven days and then has seven days off.
The drug causes sore hands and feet, sickness, diarrhoea and fatigue 'so deep sleep doesn’t repair you’, she says. 'On bad days I can barely walk and there are phases where my bones hurt so much that it’s disabling.’
Susan fears that once capecitabine stops working she will be on intravenous chemotherapy, 'which means hair loss, and once I lose my hair it’ll never come back because I’m on treatment until I die’.
She doesn’t like to think about what happens next. 'I spend a lot of time in denial and the times I’m not in denial I cry,’ she says.
’There is a moment during every day when you are reminded that you have cancer. It may be just listening to friends talk of their plans for the future – but you can’t make those kinds of plans and so all you can do is smile.’
Has she made a bucket list? 'Absolutely not,’ she says. 'As then I’d have to acknowledge I’m going to die and I refuse to do that.’
