One-time sigmoidoscopy fends off colorectal cancer risk for up to 2 decades

Once-only screening with flexible sigmoidoscopy appears to provide prolonged protection against colorectal cancer (CRC), reducing both incidence and mortality rates for up to 2 decades, according to the updated results of the UK Flexible Sigmoidoscopy Screening Trial (UKFSST).

Over a median follow-up of 21.3 years, the cumulative incidence of colorectal cancer was lower among men and women who were invited to undergo one-off flexible sigmoidoscopy screening than among their counterparts who did not receive such invitation (control; 3.18 percent vs 4.16 percent), with 47 fewer cases per 100,000 person-years. [Lancet Gastroenterol Hepatol 2024;doi:10.1016/S2468-1253(24)00190-0]

The same was true for colorectal cancer mortality, with 16 fewer deaths per 100,000 person-years in the screening than the control group (0.97 percent vs 1.33 percent).

In Cox models, flexible sigmoidoscopy screening was associated with a more than 20-percent reduction in the risk of incident CRC (hazard ratio [HR], 0.76, 95 percent confidence interval [C], 0.72–0.81) and related mortality (HR, 0.75, 95 percent CI, 0.67–0.83).

The reduction in CRC incidence and mortality mostly occurred in the distal colorectum, with a risk decrease of 41 percent (HR, 0.59, 95 percent CI, 0.54–0.64) and 45 percent (HR, 0.55, 95 percent CI, 0.47–0.64), respectively.

In subgroup analyses, men obtained greater protection against the risk of CRC incidence with screening as opposed to women (HR, 0.70, 95 percent CI, 0.65–0.76 and HR, 0.86, 95 percent CI, 0.79–0.93; p=0.0007 for interaction). There was no age-related difference.

The analysis included 170,432 men and women aged 55–64 years at baseline who expressed in a questionnaire that they would attend flexible sigmoidoscopy screening if invited. These participants were randomly assigned to the screening group that received the invitation (n=57,099, 51 percent women) or the control group that received no further contact (n=112,927, 51 percent women). Most of the participants (71 percent) in the screening group underwent sigmoidoscopy.

Health economic benefits

The previous 17-year follow-up of UKFSST showed risk reductions of 26 percent (HR, 0.74, 95 percent CI, 0.70–0.80) in all-site CRC incidence and 30 percent (HR, 0.70, 95 percent CI, 0.62–0.79) in all-site CRC mortality. The risk of distal CRC incidence and mortality decreased by 41 percent (HR, 0.59, 95 percent CI, 0.54–0.64) and 46 percent (HR, 0.54, 95 percent CI, 0.45–0.65), respectively. [Lancet 2017;389:1299-1311]

“Our new analyses show, for the first time, a considerable and sustained effect of flexible sigmoidoscopy screening in reducing the burden of CRC over 21 years, approximately 5 years beyond what was shown in our previous publication and the other flexible sigmoidoscopy trials,” the investigators said. “These findings have important implications for the cost-effectiveness of flexible sigmoidoscopy as a screening tool.” [Lancet 2017;389:1299-1311; Ann Intern Med 2018;168:775-782; Lancet Gastroenterol Hepatol 2019;4:101-110; Ann Intern Med 2022;175:36-45]

While the upfront costs are higher than that of stool-based tests, the extended protection that flexible sigmoidoscopy affords could yield significant health economic benefits, the investigators explained. Notably, the sustained reduction in CRC risk, particularly among the elderly population at heightened vulnerability (age ≥80 years), underscores the value of the procedure.

“That a one-time screening procedure could have such a lasting impact on public health over 21 years is impressive,” they added.

The investigators stated that they intend to conduct further analyses with an additional 5-year follow-up period to evaluate the durability of the observed protective effects and to assess whether protection extends until all cohort members reach 80 years of age.