A breast cancer diagnosis almost always comes as a shock. But when Patricia Copestake was told she had the disease, she had every reason to be more stunned than most.

Just a couple of months earlier, the 57-year-old mother-of-seven had attended a routine mammogram – an X-ray scan offered to all women aged 50 to 70 every three years to detect early-stage breast cancer – and had been given the all-clear.

Subsequently, when she had seen her GP about an area of her left breast that felt firmer than the rest, she was reassured by the doctor it wasn’t anything serious.

Not completely convinced, Patricia pushed for further tests and was referred to a breast clinic.

Another mammogram was clear – but, as is standard practice, she was given an ultrasound scan.

‘The sonographer placed the machine on my breast, and then reached for the button to call the consultant in,’ recalls Patricia. ‘I knew they’d found something.’

Astonishingly, the tumour was the size of a golf ball. Patricia was immediately booked in for surgery and underwent other cancer treatments. She says: ‘Once I was given the diagnosis, I started thinking to myself – how did they miss this?’

Desperate for answers, Patricia sent her previous mammograms to a private doctor, who pointed out a small note at the bottom of the X-ray: ‘75 per cent dense tissue.’

She adds: ‘I felt stupid for not knowing what that meant.’

Breast density refers to the ratio of fat to glandular and connective tissue – the less fat, the denser the breast. And as breast tissue shows up white on a mammogram – as do tumours – the more tissue, the less effective the scan.

Patricia says: ‘The consultant explained what dense breasts were and why they were the reason my mammogram failed to pick up the tumour.

‘I’ve had four mammograms over the years. Suddenly I realised that this had been known about for years but no one had informed me. I was horrified.’

More than 40 per cent of women have dense breasts – yet in Britain, unlike the US and most of Europe, they are simply not told.

A recent survey commissioned by UK healthcare provider GenesisCare found that 92 per cent of British women are unaware of the density of their breast tissue or the increased risk it carries.

Last year The Mail on Sunday was among the first to raise the alarm over the NHS’s outdated screening practice, which neither informs women of their breast density nor offers supplemental scans.

Campaigners warn that women with dense breasts are slipping through the net. Now a landmark study has concluded that the NHS breast cancer screening programme needs urgent reform.

Researchers from the University of Cambridge and Addenbrooke’s Hospital estimate more than 3,500 cancers are going undetected by mammograms each year, but adding additional screening methods could triple detection rates. Experts say the fix is inexpensive, requires no new equipment and could save hundreds of lives annually.

‘There’s always a balance – we have to be mindful of both the benefits and potential harms when making changes to screening,’ says Dr Fiona Gilbert, professor of radiology at the University of Cambridge and lead author of the study. ‘But we’re now at a point where the evidence clearly shows we should be doing more for women with dense breasts. Women need to be made aware.’

Around 56,000 women are diagnosed with breast cancer in Britain each year, making it the most common cancer in the country. While nine in ten survive, the disease still claims more than 11,000 lives annually.

Breast screening is a cornerstone in the fight against the disease, aiming to detect tumours early when they are easier to treat.

But for women with dense breasts, the programme is falling short.

Not only are dense breasts harder to scan – masking tumours on mammograms – they also carry a higher risk of developing cancer in the first place.

For the third of women with moderately dense breasts, the risk is four times higher. For the 10 per cent with the densest breast tissue, it can rise up to six-fold.

Despite this, if a woman is found during a routine scan to have dense breasts, it is not even recorded in her medical notes.

Campaigners argue that informing women of their breast density is vital – helping them understand their overall risk and take action to reduce it.

This might include maintaining a healthy weight, limiting alcohol or opting for additional scans – measures that could help catch cancers earlier and improve survival.

Campaigner Cheryl Cruwys, 58, says that despite it being known for years that women with dense breasts would benefit from better screening, women are still coming to her with a cancer diagnosis and the same despairing complaint: ‘If only I’d known.’

While living in France in 2016, Cheryl was diagnosed with early-stage breast cancer, and credits the early detection to the country’s standard practice of performing supplemental screening on dense breast tissue.

Now, she believes, the latest study could mark ‘an important step forwards for UK women’.

The new trial, published in the Lancet medical journal last month, was carried out on 9,361 women across the UK who have dense breasts and appeared cancer-free on a regular mammogram.

Researchers tested two additional scanning methods designed to detect cancer in dense breast tissue.

The first, contrast-enhanced mammography (CEM), involves injecting a dye to make blood vessels more visible on the scan.

The second, abbreviated magnetic resonance imaging (AB-MRI), offers a quicker alternative to standard MRI.

Among the women, CEM detected an additional 19 cancers per 1,000, while AB-MRI picked up 17.

A third method – a form of ultrasound – was also trialled. While it did detect additional cases, it was less effective, identifying just four extra cancers per 1,000 women.

The researchers concluded that by adding either CEM or AB-MRI to current screening practices, an extra 3,500 breast cancers could be detected each year, potentially saving around 700 lives.

For Professor Zoe Winters, senior consultant breast cancer surgeon at London Breast Health, changing the NHS breast screening programme in light of the new findings seems a no-brainer.

She says women at her private breast clinic are both informed of their breast density and automatically given further screening – usually an ultrasound, but she will likely now look to use CEM as well.

She adds: ‘I make sure women with the densest breasts get an ultrasound and 3D mammogram [which uses multiple X-ray images from different angles to create a layered, three-dimensional picture, making it easier to spot hidden tumours] as a matter of routine – but I’m still missing cancers.

‘In the US, it’s now mandated that every woman needs to be informed of their breast density. It’s important that British women also have this knowledge.’

Professor Gilbert says it’s more about ensuring that changes to the scheme won’t cause unintentional damage. ‘It should be relatively straightforward and cost-effective to introduce contrast-enhanced mammograms on to the breast screening programme,’ she says. ‘Many screening centres and breast clinics across the country already have contrast equipment, as it comes as an add-on when you buy a mammography machine.

‘But it needs to be balanced against the risk to women – there’s always a very small chance that giving intravenous iodine will cause an allergic reaction.’

She points out that policymakers are also concerned about overdiagnosis – treating tumours that would not have progressed to a life-threatening stage in the patient’s lifetime, adding: ‘Some people will correctly argue that by detecting some of these additional tumours, we’re finding lumps that would maybe never have caused harm.’

But, she says, the weight of evidence is for screening, particularly as finding cancers early gives most women a much better chance of survival.

And finally, some argue that informing women of their breast density could cause unnecessary worry, especially if further testing isn’t available. But at the end of the day, Prof Gilbert says, women should be allowed to choose.

‘As long as women are properly informed of the risks of contrast-enhanced mammograms, then it should be their choice to accept the scan or not,’ she says.

‘Changes need to be made to the breast screening programme. We just have to figure out the best way to roll these out.’

For Deborah King, 60, these could not come any sooner. After discovering a 1.5in (4cm) tumour in her left breast just two months after an all-clear mammogram, she endured a gruelling two years of surgeries and treatment.

She says: ‘I could have died. As a single parent with a teenage daughter, that’s a terrifying thought. I feel like I fell through the net.’

Now graphic designer Deborah tells all her friends to request their breast density information when they attend mammograms. ‘Some are told and some aren’t,’ she says. ‘But it’s worth a try.’

If this doesn’t work, Deborah advises, email your hospital an access request to your mammogram results, and they have to send the scans within 30 days.

She adds: ‘How are we supposed to make informed decisions about our health if we’re not being informed about this? Particularly for menopausal women deciding whether to take hormone therapy, which can increase the risk of cancer. It’s costing women their lives.’

Patricia agrees, adding. ‘I asked my doctor at the time why they hadn’t told me about my breast density, and they said they didn’t like to worry ladies unnecessarily.

‘But I’d rather worry for a few weeks and be told it’s OK than not worry and die because my cancer is found once it’s too late for treatment. It’s an easy choice, in my opinion.’