Men benefit more than women from once-only sigmoidoscopy screening

By Wayne Kuznar, for MDLinx
Published May 16, 2018

Key Takeaways

Among persons 50 to 64 years old, a single sigmoidoscopy screening reduces the incidence of colorectal cancer (CRC) and mortality in men but not in women, according to data from a randomized trial conducted in Norway.

After up to 17 years of follow-up, CRC incidence was reduced by an absolute 0.78% and CRC mortality by an absolute 0.33% in men, without any effect on incidence or mortality in women, found Øyvind Holme, MD, PhD, associate professor, Institute of Health and Society, University of Oslo, Norway, and colleagues.

Current guidelines from the US Preventive Services Task Force recommend repeated sigmoidoscopy screening at 5- to 10-year intervals. “Our findings indicate that once-only sigmoidoscopy screening reduces the risk for CRC incidence over 17 years by 34% in men but does not reduce risk in women,” they wrote in Annals of Internal Medicine. “For CRC mortality, we observed a 37% reduction in men but little or no reduction in women.”

Between 1999 and 2001, all persons 50 to 64 years old living in Oslo and Telemark County, Norway, were identified through a population registry. A random sample of those without a personal history of CRC was offered one-time flexible sigmoidoscopy or the combination of one-time only flexible sigmoidoscopy and a single fecal occult blood test (FOBT). Those with positive screening results were offered colonoscopy.

There were 20,552 in the screening group and 78,126 controls. Men made up about half (49.8%) of the study population. In the screening group, 10,271 participants were randomized to sigmoidoscopy and 10,281 to the combination of sigmoidoscopy and FOBT. Screening adherence rates were 64.7% in women and 61.4% in men.

A total of 2,520 (19.5%) screened subjects (16.2% of women and 22.9% of men) had colonoscopy for positive screening results. The screening attendance rate was higher for women than men (64.7% vs. 61.4%). Median follow-up was 14.8 years.

In women, the 15-year absolute risk for CRC was 1.86% in the screening group and 2.05% in the control group, which was not significant (HR 0.92, 95% CI 0.79-1.07). The 15-year absolute risk for CRC death was nearly identical at 0.60% in the screening group and 0.59% in the control group. Both the CRC incidence and mortality rates differed little between the screening and control groups with tumor location (distal vs proximal colon) or screening method (sigmoidoscopy alone vs with FOBT).

In men, the absolute risk for CRC was 1.72% in screened subjects and 2.50% in the controls (HR 0.66, 95% CI 0.57-0.78; P for heterogeneity 0.004). The absolute risk for death from CRC in men was 0.49% in the screened group and 0.81% in controls (HR 0.63, 95% CI 0.47-0.83; P for heterogeneity 0.014).

The effect of sigmoidoscopy screening in men “lasted beyond what we have previously reported, and we found a strong trend toward reduction in all-cause mortality in men screened by sigmoidoscopy,” the authors wrote. The all-cause mortality rate in men who were screened was 1,572 deaths per 100,000 person-years and 1,638 in the control group (HR 0.96, 95% CI 0.91-1.00).

“In comparison, the UK Flexible Sigmoidoscopy Screening trial found that once-only sigmoidoscopy screening was effective in both women and men after 17 years of follow-up, although less so in women, which is consistent with our findings,” they added.

The reason for the limited or no effect of sigmoidoscopy screening in women is unclear, although the investigators postulate that screening may benefit men preferentially because they have a higher risk of CRC.

“Alternatively, these findings may reflect that women who were screened had a different CRC risk profile from men (screening attendance rates in our study were higher for women than men),” they wrote. “Men also have a higher prevalence of adenomas at sigmoidoscopy screening, and accordingly, men were more often referred for colonoscopy.”

The study’s results may have implications for future screening recommendations and trial design that include sex-stratified evaluations and sample size calculations, the authors advised.

This research was funded by the Norwegian government and the Norwegian Cancer Society.

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