Thousands of bowel cancer cases are being missed due to “unacceptable” testing failures, research in the BMJ shows.
The UK research found that some providers carrying out colonoscopies were three times as likely as others not to spot signs of disease.
At the worst units, almost one in ten cases which turned out to be bowel cancer were not picked up during the tests, the study led by the University of Leeds found.
Researchers said that almost 4,000 more cases could have been prevented or treated sooner had there been better screening over a nine year period tracked.
They warned of “unacceptable variation” between units, with the worst results seen at private providers given NHS contracts to carry out the tests.
Bowel cancer is the fourth most common cancer in the UK and the second biggest cancer killer.
More than 42,000 people are diagnosed with bowel cancer every year in the UK.
The study involved more than 120,000 men and women who underwent colonoscopy – the main test used to detect bowel cancer – at all screening providers in England.
It examined rates of cancer among those who were diagnosed at least six months after being given the all clear.
The study found an overall improvement between 2005 and 2013. In 2005, 9 per cent of cases diagnosed with bowel cancer had received a negative result in a colonoscopy between six months and three years earlier – meaning they could potentially have been diagnosed far earlier.
By 2013, the figure was 6.5 per cent.
If the earlier figure matched the later standard, 3,900 cases of bowel cancer would have been spotted earlier, or even prevented, over the nine year period, researchers said.
Even now, some providers have rates of “post-colonoscopy colorectal cancers” three times higher than those of others, the study found.
The best rates – of 3.6 per cent – were provided by NHS screening units, while the worst – of 9.3 per cent – were seen at independent providers being used by the health service.
The study found that women, those aged 80 and over and patients suffering inflammatory bowel disease were the most likely to receive a diagnosis of bowel cancer in the years after a colonoscopy with a negative result.
Researcher Roland Valori, Consultant Gastroenterologist from Gloucestershire Hospitals NHS Foundation Trust, said: “We are seeing unacceptable variation in post colonoscopy bowel cancers between providers in the English NHS and this variation in quality needs to be addressed urgently.”
The British Society of Gastroenterology say post-colonoscopy bowel cancers should be used as a benchmark for the quality of the testing service.
Lead author Dr Nick Burr, from the University of Leeds, said: “We need a targeted improvement programme to reduce this variation.”
“Ensuring we have uniform high standards for colonoscopies will help us reduce the number of post-colonoscopy cancers further, and improve mortality from this preventable disease.”