Receiving one sigmoidoscopy significantly reduces long-term incidence of colorectal cancer (CRC) in both men and women, a study found.
Researchers analyzed four randomized trials from Norway, the United States, the United Kingdom, and Italy that compared sigmoidoscopy screening to usual care and had a minimum of 15 years of follow-up. Predefined primary outcomes were CRC incidence and mortality after sigmoidoscopy screening compared with usual care. Only participants ages 55 to 64 years at enrollment were selected for analyses because these age groups were included in all four trials. Secondary outcomes were all-cause mortality along with incidence and mortality by cancer site (distal vs. proximal colon), sex, and five-year age group (55 to 59 years vs. 60 to 64 years at enrollment). Results of the study were published by Annals of Internal Medicine on Oct. 11.
The study included 137,493 patients in the screening group and 137,459 in the usual care group. Screening attendance ranged from 58% to 84%. After 15 years, the rate difference for CRC incidence was 0.51 case (95% CI, 0.40 to 0.63 case) per 100 persons and the incidence rate ratio (IRR) was 0.79 (95% CI, 0.75 to 0.83). The rate difference for CRC mortality was 0.13 death (95% CI, 0.07 to 0.19 death) per 100 persons, and the mortality rate ratio (MRR) was 0.80 (95% CI, 0.72 to 0.88).
Women benefited less from sigmoidoscopy screening than men for CRC incidence (IRR, 0.84 [95% CI, 0.77 to 0.91] vs. 0.75 [95% CI, 0.70 to 0.81], respectively; P=0.032 for difference) and mortality (MRR, 0.91 [95% CI, 0.77 to 1.17] vs. 0.73 [95% CI, 0.64 to 0.83], respectively; P=0.025 for difference). There was no statistically significant difference in screening effect between persons ages 55 to 59 years and those ages 60 to 64 years.
According to the authors, possible explanations for the difference in CRC incidence between men and women include differences in the quality of bowel preparation, more technically challenging procedures in women, and a higher incidence and larger proportion of proximal colon cancer in women. Adherence to sigmoidoscopy screening was also slightly lower in women than men in all but one trial. Colonoscopy contamination of the usual care groups could also differ if thresholds for symptoms triggering a colonoscopy vary between women and men, the authors noted.
“Our study indicates that there is a long-term reduction in CRC incidence and mortality after 1 sigmoidoscopy … which may prompt guideline makers to reconsider endoscopic screening intervals,” the authors wrote.