Single bowel screening test can cut cancer risk by a quarter over two decades

New data from Imperial reveal that a single screening test can reduce bowel cancer deaths by 25%, with protective effects lasting 21 years.

Published in The Lancet Gastroenterology and Hepatology, the study reveals that a single flexible sigmoidoscopy screening (flexi-sig) can reduce the chance of developing bowel cancer by 24% and the chance of dying from bowel cancer by 25%, for up to 21 years after screening.

I hope that the data will contribute to the ongoing discussion around bowel cancer screening guidelines, emphasising the need for widespread implementation of effective screening programmes. Professor Amanda Cross Department of Surgery & Cancer

The research was conducted by the Department of Surgery and Cancer’s Cancer Screening and Prevention Research Group (CSPRG) and funded by the National Institute for Health and Care Research and Cancer Research UK.

The trial included 170,000 participants aged 55-64 years who were recruited from 1994 to 1999 and were randomly divided into two groups: 1) those who were invited for screening with flexi-sig (57,000 people); and 2) control participants who were not invited for flexi-sig (113,000 people).

Of those invited for flexi-sig, 41,000 (approximately 70%) had the test. The research team continued to follow-up the two groups and compared them to investigate if a single flexi-sig reduced the risk of getting bowel cancer and reduced the risk of dying from this disease.

First author and Medical Statistician in the CSPRG, Ms Kate Wooldrage, said: "Our findings that a one-off flexi-sig screening test can offer long-term protection against bowel cancer, and have an impact on public health lasting over two decades, are impressive.”

Bowel cancer is the fourth most common cancer and the second most common cause of cancer deaths each year in the UK.

It is already well documented that screening for bowel cancer in individuals without symptoms can lower the chance of dying from bowel cancer and can help prevent it developing in the first place, but this is the first trial to show such a long-lasting effect.

Differences in screening effectiveness by sex

Flexi-sig is a screening test which involves a camera attached to a thin tube being passed through the bottom to look at the inside of the bowel.

During the test, polyps (small growths on the lining of the bowel that can develop into cancer) can be removed or bowel cancers can be detected at an earlier stage. In contrast to colonoscopy, another common bowel test, flexi-sigs are quicker and less invasive because they look at a smaller portion of the bowel.

Interestingly, the study also showed that flexi-sig screening appears to be more effective in men, who benefited from a 30% decrease in risk of bowel cancer, compared to women who experienced a 14% decrease.

This is likely because men tend to develop bowel cancer near the end of their bowels and rectum (known as distal bowel cancer) where a flexi-sig can easily reach, whereas women are more likely to develop bowel cancer further up in the bowel, out of range of a flexi-sig; women are also more likely to experience difficulties when having a flexi-sig.

Overall, the protective effect of flexi-sig became even more pronounced when looking at just distal bowel cancers, as there was a 41% reduction in the risk of distal bowel cancer and a 45% reduction in deaths from distal bowel cancer.

Speaking about the potential impact of the study findings, last author and Professor of Cancer Epidemiology in the Department of Surgery and Cancer, Professor Amanda Cross said: "Screening procedures hold immense potential to reduce cancer incidence and mortality. I hope that the data will contribute to the ongoing discussion around bowel cancer screening guidelines, emphasising the need for widespread implementation of effective screening programmes."

For more information on the study, visit the UK Flexible Sigmoidoscopy Screening Trial web page.

This research is supported by funding from the National Institute for Health and Care Research (NIHR) Imperial Biomedical Research Centre (BRC), a translational research partnership between Imperial College London and Imperial College Healthcare NHS Trust, which was awarded £95m in 2022 to continue developing new experimental treatments and diagnostics for patients.

'Long-term effects of once-only flexible sigmoidoscopy screening on colorectal cancer incidence and mortality: 21-year follow-up of the UK Flexible Sigmoidoscopy Screening randomised controlled trial' by
Kate Wooldrage, Emma C Robbins, Stephen W Duffy, Amanda J Cross is published in The Lancet Gastroenterology & Hepatology, 2024