Study Finds Sigmoidoscopy Screening Reduces Colon Cancer Risk in Men but Not Women

Key Points

  • Flexible sigmoidoscopy reduced colorectal cancer incidence in men by 34% and reduced their risk of death from the cancer by 37%. However, there was little or no reduction in colorectal cancer risk or mortality among women screened with sigmoidoscopy compared to those that where not screened.
  • The findings suggest that current guidelines recommending that women get screened for colorectal cancer with sigmoidoscopy should be reconsidered.
  • These results may have implications for future screening recommendations and clinical trial design in which sex-stratified evaluations and sample size calculations should be considered.

The U.S. Preventive Services Task Force recommends several screening tests for colorectal cancer (CRC) in adults aged 50 to 75, including fecal occult blood testing, sigmoidoscopy, or colonoscopy. According to the American Cancer Society, in 2017, there were an estimated 95,520 cases of colon cancer and nearly 40,000 cases of rectal cancer diagnosed in the United States, and an estimated 27,150 men and 23,310 women died from their disease. Screening can reduce colorectal morality both by decreasing incidence of the cancer and increasing the likelihood of survival. 

However, a large randomized controlled study in Norway examining the effectiveness of flexible sigmoidoscopy screening after 17 years of follow-up in women and men has found that the screening method reduced colorectal cancer (CRC) incidence by 34% and mortality by 37% in men, but had little or no effect in women. The study’s results may have implications for future screening recommendations and clinical trial design in which sex-stratified evaluations and sample size calculations should be considered. The study by Holme et al is published in the Annals of Internal Medicine.

Study Methodology

Between 1999 and 2000, researchers from the Cancer Registry of Norway and the University of Oslo randomly assigned 98,678 adults ages 55 to 64 that were eligible for analyses; 20,552 in the screening group, and 78,126 in the control group. In the screening group, 10,271 participants were randomly assigned to sigmoidoscopy screening and 10,281 to the combination of sigmoidoscopy and fecal occult blood testing. Men accounted for 49.8% of the study population. The median follow-up was 14.8 years for both incidence and mortality of colorectal cancer.

Study Findings

The researchers found that the absolute risks for colorectal cancer in women were 1.86% in the screening group and 2.05% in the control group (risk difference = 0.19%, 95% confidence interval [CI] = 0.49%–0.11%; hazard ratio [HR] = 0.92, CI = 0.79–1.07). In men, the corresponding risks were 1.72% and 2.50%, respectively (risk difference = 0.78%, CI = 1.08%–0.48%; hazard ratio = 0.66, CI, 0.57–0.78) (for heterogeneity = .004). The absolute risks for death of colorectal cancer in women were 0.60% in the screening group and 0.59% in the control group (risk difference = 0.01%, CI = 0.16%–0.18%; HR = 1.01, CI = 0.77–1.33). The corresponding risks for death of colorectal cancer in men were 0.49% and 0.81%, respectively (risk difference = 0.33%, CI = 0.49%–0.16%; HR = 0.63, CI = 0.47–0.83) (for heterogeneity = .014). 

“Our results may have implications for future screening recommendations and trial design, where sex-stratified evaluations and sample size calculations should be considered. We further believe that communicating absolute rather than relative risk reductions…would be preferable during shared decision-making with patients,” concluded the study researchers.

Øyvind Holme, MD, PhD, of the Institute of Health and Society, Department of Health Management and Health Economics at the University of Oslo, is the corresponding author of this study.

Funding for this study was provided by the Norwegian government and the Norwegian Cancer Society.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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