A collaboration between a team at King's College London led by Peter Sasieni and a QMUL-based group led by Stephen Duffy collected data from over 14,000 people with bowel cancer and over 29,000 people who did not have bowel cancer.

In 2006, the NHS began offering bowel cancer screening with a guaiac stool test, following clinical trials that showed screenings could reduce the number of people dying from bowel cancer. The test detects invisible blood in an individual's stool samples, though this has since been replaced with an improved stool test.

The study reviewed NHS Bowel Cancer Screening Program (NHSBCSP) of guaiac test data to determine whether people who participated in bowel cancer screening were more or less likely to develop bowel cancer than people who did not participate. The study looked at participation separately for people with different stages of bowel cancer.

"The results […] suggest that people screened previously reduced their risk of dying from bowel cancer by about 20%. Bowel cancer screening results in early detection of cancer and prevents people from suffering from the effects of advanced bowel cancer and its treatment," says Sasieni, Academic Director of King's Clinical Trials Unit and Professor of Cancer Prevention

The results, published in the Journal of the National Cancer Institute, found that screened people were at roughly the same risk of being diagnosed with bowel cancer as people who did not get a screening. This was to be expected because guaiac stool screenings aim for early diagnosis but cannot prevent bowel cancer. However, there were concerns that screening would over-diagnose unproblematic cancers. According to the authors, this observation shows that there was not a significant problem with over-diagnosis in the NHSBCSP.

Another important observation was that people with advanced bowel cancer were much less likely to participate in screening when compared to people without bowel cancer. And this association persists after adjusting for other differences between people who do and do not participate. This is an important finding as it suggests that screening participation significantly reduces the risk of dying from bowel cancer.

The authors estimated that the risk of developing advanced bowel cancer was reduced by 30% among people who were screened. As the NHS Long-Term Plan aims to increase the proportion of early cancer diagnosis from just over 50% to 75% by 2028, the early detection of advanced bowel cancer is vital for achieving this goal. By preventing advanced bowel cancer, the authors suggest that the NHSBCSP is on track to reduce bowel cancer mortality.

"Our results suggest that the bowel screening program in England is reducing the risk of fatal bowel cancer among those who participate. I hope these results will encourage more individuals to take up their screening offer when invited," says Alejandra Castanon, Senior Epidemiologist