Once-off screening test slashes bowel cancer risk

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A single flexible sigmoidoscopy provides substantial protection from colorectal cancer diagnosis and death, with protection lasting at least 17 years, found a large UK analysis.

The researchers, funded through a Medical Research Council (MRC) and National Institute for Health Research (NIHR) partnership and Cancer Research UK, found that the test – which examines the lower part of the large bowel – prevented more than half of potential bowel cancers from developing in that area and two thirds of deaths were avoided.

Bowel scope uses a tiny camera attached to a thin flexible tube to examine a specific part of the bowel but was still found to prevent 35% of bowel cancers overall and to prevent 40% of deaths.

The team followed more than 170,000 people for 17 years on average and more than 40,000 had the bowel scope test. It is the longest study ever done on the effectiveness of the test.

Bowel scope can stop cancer before it starts by finding small growths, called polyps, on the bowel wall. If left untreated polyps may become cancerous, but those found during bowel scope can usually be removed there and then.

Professor Wendy Atkin, Cancer Research UK’s bowel screening expert and lead author based at Imperial College London, said: “We know the bowel scope test has huge benefits for older people. Although no screening test is perfect, this study shows that bowel scope is effective in reducing cancer deaths for at least 17 years.

“Bowel cancer can be prevented. And the bowel scope screening test is a great way to reduce the number of people diagnosed with the disease so it’s vital that no one misses out on the opportunity to get the test.”
Julie Sharp, Cancer Research UK’s head of health information said: “Like other types of screening, bowel scope is meant for people without symptoms. It’s a great way to help reduce the number of people developing or dying from bowel cancer, but it can’t pick up everything.

“So it’s still important to take part in the rest of the bowel screening programme and not ignore the home testing kits when they arrive. And whatever your screening history tell your doctor if you notice any unusual or lasting changes such as blood in your poo or a change in bowel habit.”

Emma Greenwood, Cancer Research UK’s director of policy, said: “In England the government has committed to rolling out this test but there is a shortage of trained staff to carry it out. A training scheme is underway but it’s important that there are enough newly trained specialists to meet the growing demand for these life-saving tests.”

Background: Colorectal cancer is the third most common cancer worldwide. Previous analyses have only reported follow-up after flexible sigmoidoscopy for a maximum of 12 years. We aimed to examine colorectal cancer incidence and mortality after a single flexible sigmoidoscopy screening and 17 years of follow-up.
Methods: In this multicentre randomised trial (UK Flexible Sigmoidoscopy Screening Trial), done between Nov 14, 1994, and March 30, 1999, 170 432 eligible men and women, who had indicated on a previous questionnaire that they would probably attend screening if invited, were randomly assigned (1:2) to an intervention group (offered flexible sigmoidoscopy screening) or a control group (not contacted). Randomisation was done centrally in blocks of 12, and stratified by trial centre, general practice, and household type. The nature of the intervention did not allow the staff to be masked to arm of the trial; however, randomisation was done in batches so that the control group and participants not yet randomised were unaware of their allocation status. The primary outcomes were incidence and mortality of colorectal cancer. Hazard ratios (HRs) and 95% CIs for colorectal cancer incidence and mortality were estimated for intention-to-treat and per-protocol analyses. The trial is registered with ISRCTN, number 28352761.
Findings: Our cohort analysis included 170 034 people: 112 936 in the control group and 57 098 in the intervention group, 40 621 (71%) of whom were screened and 16 477 (29%) were not screened. During screening and a median of 17·1 years’ follow-up, colorectal cancer was diagnosed in 1230 individuals in the intervention group and 3253 in the control group, and 353 individuals in the intervention group versus 996 individuals in the control group died from colorectal cancer. In intention-to-treat analyses, colorectal cancer incidence was reduced by 26% (HR 0·74 [95% CI 0·70–0·80]; p<0·0001) in the intervention group versus the control group and colorectal cancer mortality was reduced by 30% (0·70 [0·62–0·79]; p<0·0001) in the intervention group versus the control group. In per-protocol analyses, adjusted for non-compliance, colorectal cancer incidence and mortality were 35% (HR 0·65 [95% CI 0·59–0·71]) and 41% (0·59 [0·49–0·70]) lower in the screened group.
Interpretation: A single flexible sigmoidoscopy continues to provide substantial protection from colorectal cancer diagnosis and death, with protection lasting at least 17 years.

Wendy Atkin, Kate Wooldrage, D Maxwell Parkin, Ines Kralj-Hans, Eilidh MacRae, Urvi Shah, Stephen Duffy, Amanda J Cross

Cancer Research UK material
The Lancet article summary

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