February 23, 2017
3 min read

One sigmoidoscopy exam protects against colorectal cancer for 17 years

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A single flexible sigmoidoscopy examination reduced the risk for colorectal cancer by more than a third, and provided continued protection against CRC diagnosis and mortality for at least 17 years, according to results from the U.K. Flexible Sigmoidoscopy Screening Trial.

Flexible sigmoidoscopy is an expensive and invasive test, but it has three distinct advantages over blood and stool tests,” Wendy Atkin, PhD, of the Cancer Screening and Prevention Research Group, department of surgery and cancer, Imperial College London, and colleagues wrote. “First, it is highly sensitive for small lesions and so neoplasia is detectable at a very early stage. Second, most lesions can be removed at the time of screening, so the screening in most cases is both diagnostic and therapeutic. Last, results from this study suggest that the test might not need to be repeated.”

Because follow-up was limited to 12 years in prior studies, Atkin and colleagues sought to evaluate CRC incidence and mortality up to 17 years after one flexible sigmoidoscopy screening examination. To do so they performed a multicenter randomized trial between 1994 and 1999, in which they randomly assigned 170,432 eligible participants to either be invited to undergo sigmoidoscopy (n = 57,098) or not (n = 112,936).

Overall, 71% of the intervention group underwent sigmoidoscopy screening. Throughout a median of 17.1 years of follow-up, 1,230 participants in the intervention group received a CRC diagnosis and 353 died of their cancer, compared with 3,253 and 996 of the controls, respectively.

Intention-to-treat analyses showed the intervention group had a 26% lower risk for CRC (HR = 0.74; 95% CI, 0·7–0·8) compared with controls and a 30% lower risk for CRC mortality (HR = 0.7; 95% CI, 0·62–0·79).

Further, per-protocol analyses adjusting for non-compliance showed the intervention group had a 35% lower incidence of CRC (HR = 0.65; 95% CI, 0·59–0·71) and a 41% lower risk for CRC mortality (HR = 0.59; 95% CI, 0·49–0.7).

“Our results show that a single flexible sigmoidoscopy examination in people aged between 55 years and 64 years confers a substantial protection from colorectal cancer diagnosis and death lasting at least 17 years,” Atkins and colleagues concluded. “We will continue to follow-up the trial cohort enabling us to monitor the long-term effects of flexible sigmoidoscopy screening on colorectal cancer incidence and mortality, and to further examine the longevity of effect.”

Screening for CRC using even a single flexible sigmoidoscopy “is a resource-conserving strategy that, as shown in the study ... seems to achieve much of the potential of colorectal cancer prevention, but one which also misses a substantial fraction of potentially preventable or curable cancers,” Paul F. Pinsky, MD, of the National Cancer Institute in Bethesda, Maryland, wrote in a related editorial. “Assessment of screening strategies involving flexible sigmoidoscopy, colonoscopy, or stool-testing generally compare screening efficacy, in terms of colorectal cancer cases or deaths prevented, with the costs and resource utilizations of the screening programme. These latest long-term results from the UKFSST should provide additional data for researchers to re-assess these strategies.”

Government estimates expect it will take at least 3 years before flexible sigmoidoscopy will be offered to all eligible individuals aged 55 years in England while Scotland, Wales and Northern Ireland have not yet committed to implementing this strategy within their bowel screening programs, according to a press release from Cancer Research UK.

“In England the government has committed to rolling out this test but there is a shortage of trained staff to carry it out,” Emma Greenwood, Cancer Research UK’s director of policy, said in the press release. “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.” – by Adam Leitenberger

Disclosures: Atkin reports she was the recipient as principal investigator of all study funding. Pinsky reports no relevant financial disclosures.