Single sigmoidoscopy screening may reduce colorectal cancer, mortality in men but not women

Patients in Norway were randomly assigned to flexible sigmoidoscopy with and without additional fecal blood testing (with colonoscopy offered if results were positive) and were compared to patients offered no screening.

Screening with sigmoidoscopy significantly reduced men's risk of colorectal cancer incidence and mortality over the subsequent 15 years, but it had little or no effect in women, according to a recent study.

The trial included 98,678 Norwegians ages 50 to 64 years with no history of colorectal cancer at baseline. Between 1999 and 2001, 20,552 patients were randomized to flexible sigmoidoscopy with and without additional fecal blood testing (with colonoscopy offered if results were positive), and they were compared to 78,126 patients offered no screening. Median follow-up was 14.8 years. Results were published by Annals of Internal Medicine on April 24.

The absolute risk for colorectal cancer was significantly lower among men in the screening group compared to controls (1.72% vs. 2.50%; risk difference, −0.78 percentage point [95% CI, −1.08 to −0.48 percentage points]; hazard ratio [HR], 0.66 [95% CI, 0.57 to 0.78]; P=0.004 for heterogeneity). However, this difference was not significant in women (1.86% vs. 2.05%; risk difference, −0.19 percentage point [95% CI, −0.49 to 0.11 percentage point]). Similarly, men saw a decrease in risk of colorectal cancer mortality with screening (0.49% vs. 0.81%; risk difference, −0.33 percentage point [95% CI, −0.49 to −0.16 percentage point]; HR, 0.63 [95% CI, 0.47 to 0.83]; P= 0.014 for heterogeneity), while women did not (0.60% vs. 0.59%).

Previous research has suggested a smaller effect of sigmoidoscopy screening in women than men, the study authors noted. The causes of this difference are unknown, although the study authors offered several theories, including sex differences in the risk for colorectal cancer, more adenomas leading to colonoscopy among men, and differences in the quality of screening, although they noted that none were likely to explain the study's findings. They recommended consideration of sex-specific guidelines for colorectal cancer screening.

An accompanying editorial noted that the study's most innovative finding was the effectiveness of a single flexible sigmoidoscopy at reducing colorectal cancer incidence for 15 to 17 years in men, since current recommendations call for such screening every 5 to 10 years. The editorialists also offered an alternative explanation for the lack of effect in women: Men have peak incidence of colorectal cancer at a younger age.

More research is needed to determine if women could benefit from one-time sigmoidoscopy screening at a later age, the editorial said, adding that studies are also underway comparing colonoscopy, fecal immunochemical testing, and no screening. “Until these studies are completed, the only screening strategies supported by randomized controlled trials remain regular flexible sigmoidoscopy and fecal occult blood testing,” the editorialists wrote.