A blood test that detects tiny fragments shed by bowel cancer cells could help catch the disease at its earliest stage, increasing the chances of survival.
The test scans the bloodstream, looking for traces of DNA that are released when cancer cells die and are replaced by new ones.
These traces can often be found in the blood long before the symptoms of bowel cancer – such as blood in the stools or a marked change in bowel habits – become apparent.
A study of more than 7,000 patients with bowel cancer carried out in the US showed the test successfully detected the disease in more than 83 per cent of them.
The research was done by Massachusetts General Hospital and Harvard Medical School and published in the New England Journal of Medicine last year.
Three months later, the US Food and Drug Administration, which vets new tests and treatments, approved the use of the Shield blood test – which took ten years to develop – for screening people in the US over 45 who are at risk of bowel cancer.
Rates of bowel cancer in the UK are rising, particularly among younger adults.
Risk factors include having a close relative with the disease, obesity, sedentary lifestyles, smoking and drinking too much alcohol.
Bowel cancer rates are on the rise and it is vital to diagnose it early
Diet also contributes – eating excessive amounts of processed and red meat, for instance – and there are suggestions that highly processed foods may also be implicated, but research is ongoing.
Bowel cancer kills more than 16,000 people in the UK every year.
If caught before it has spread beyond the bowel, the five-year survival rate is around 90 per cent.
But for those diagnosed when the cancer has spread to other organs, this drops to just 10 per cent.
The concern is that too many cases are detected late: just 14.4 per cent of bowel cancer cases in the UK were diagnosed at stage 1 – with almost 30 per cent picked up at much more advanced stage 4, according to a 2020 study in the journal Gut.
The NHS already runs a bowel cancer screening programme for those aged 54 to 74.
It involves taking a small stool sample and sending it off to be tested for signs of blood which may indicate the presence of cancer or polyps – tiny growths in the bowel that are not cancer but can turn into it over time.
A similar blood test – the carcinoembryonic antigen (CEA) test – is already available on the NHS. It checks the blood for CEA, a non-specific cancer biomarker.
But it is normally only used to check how well treatment is working in certain types of cancer, particularly bowel cancer, as some studies suggest it is too inaccurate to be used to diagnose the disease.
In contrast, the Shield blood test only looks for DNA specific to bowel cancer cells.
But while it accurately spotted more than 80 per cent of bowel tumours, it also missed 16 per cent of them. The study also found it was better at detecting more advanced cancers than early ones.
Commenting on the test, Dr Lisa Wilde, director of research, policy and influencing at Bowel Cancer UK, said it could one day be an alternative method for patients who don’t like the idea of taking stool samples at home and posting them off for testing under the NHS screening programme.
‘It’s encouraging to see new tools developed to help diagnose bowel cancer at an early stage and before symptoms begin,’ she says.
‘But the NHS screening programme appears to be better than the Shield test at indicating the presence of polyps that may develop into cancers in the future and can be removed during a colonoscopy.
‘We need to know more about the accuracy of this test before it can be used on the NHS.’
