Long-Term Sigmoidoscopy Screening Reduces Colorectal Cancer Risk: 23-Year Randomized Trial Findings from Norway

Colorectal cancer remains one of the most common and deadly cancers worldwide, ranking among the top causes of cancer-related illness and death. Screening programs are widely used to detect early disease and remove precancerous growths before they develop into cancer. A major long-term randomized controlled trial published in the Annals of Internal Medicine has now provided updated evidence showing the impact of once-only sigmoidoscopy screening after 23 years of follow-up.

This article focuses on how sigmoidoscopy screening affects colorectal cancer incidence and mortality in men and women over more than two decades.

Study Overview

The study is based on the NORCCAP (Norwegian Colorectal Cancer Prevention) trial conducted in Oslo and Telemark County, Norway. It included more than 100,000 adults aged between 50 and 64 years who had no prior diagnosis of colorectal cancer.

Participants were randomly assigned into two groups:

• A screening group offered a once-only flexible sigmoidoscopy, with some participants also receiving a fecal immunochemical test (FIT)
• A control group that received no organized screening invitation

Researchers tracked participants for up to 23 years using national health registries to measure colorectal cancer incidence and deaths.

The trial was population-based, meaning participants were selected from the general population rather than volunteers, making the results highly relevant for real-world public health screening programs.

Key Findings After 23 Years

The results show that sigmoidoscopy screening provided long-term protection against colorectal cancer, especially in men.

Cancer incidence

• Men in the screening group had a colorectal cancer risk of 4.3 percent compared with 6.0 percent in the no-screening group
• This represents an absolute reduction of 1.7 percentage points
• Women had a smaller reduction, with risk decreasing from 4.7 percent to 4.2 percent

Cancer deaths

• Men in the screening group had a colorectal cancer death rate of 1.4 percent compared with 2.2 percent in the control group
• This corresponds to a meaningful reduction in mortality
• In women, no statistically significant reduction in colorectal cancer deaths was observed

Overall pattern

The study found that screening reduced distal colorectal cancers more strongly than proximal cancers. The protective effect was also more pronounced in men than in women across almost all measured outcomes.

How Sigmoidoscopy Screening Works

Flexible sigmoidoscopy is a minimally invasive procedure that allows doctors to examine the lower part of the colon and rectum. During the procedure, precancerous polyps can be identified and removed immediately.

This process reduces cancer risk in two main ways:

1. Early detection of existing cancers
2. Prevention through removal of precancerous polyps

The study suggests that these two mechanisms contribute to both early and long-term reductions in colorectal cancer deaths, particularly in men.

Important Sex Differences Observed

One of the most notable findings is the difference in outcomes between men and women.

Possible explanations discussed by researchers include:

• Higher rates of proximal colon cancer in women, which is not fully reached by sigmoidoscopy
• Differences in cancer biology between sexes
• Variation in lesion detection patterns and follow-up procedures
• Anatomical and physiological differences that may influence screening effectiveness

Although women still experienced some reduction in cancer incidence, the effect on mortality was not statistically significant.

FIT Combined with Sigmoidoscopy

Some participants received a fecal immunochemical test (FIT) alongside sigmoidoscopy. However, the study found no additional long-term benefit from combining FIT with sigmoidoscopy compared to sigmoidoscopy alone.

This suggests that the main protective effect came from the endoscopic examination rather than stool-based testing in this single-use screening model.

Public Health Implications

These findings have important implications for colorectal cancer screening programs worldwide.

Key takeaways include:

• A single sigmoidoscopy can provide long-lasting protection for more than two decades
• Screening is particularly effective in reducing colorectal cancer incidence and deaths in men
• Population-based screening programs can achieve measurable reductions in cancer burden
• The role of sigmoidoscopy should be reconsidered alongside colonoscopy and stool-based tests

Although colonoscopy is often considered the gold standard today, sigmoidoscopy remains a less resource-intensive option that can still deliver meaningful population-level benefits.

Strengths of the Study

This trial has several important strengths:

• Large sample size of over 100,000 participants
• Long follow-up period of 23 years
• Population-based randomized design
• High-quality national registry data for cancer and mortality outcomes
• High adherence rates to screening procedures

These strengths make the findings highly reliable and relevant for long-term screening policy discussions.

Limitations of the Research

Despite its strengths, the study also has limitations:

• Differences in age distribution and randomization ratios across groups
• Possible use of opportunistic screening outside the trial
• Reduced statistical power in sex-specific subgroup analyses
• Lack of complete control over all external screening behaviors over time

Researchers note that while these factors may influence precision, they are unlikely to fully explain the observed differences in outcomes.

Conclusion

This 23-year follow-up of the NORCCAP randomized trial provides strong evidence that once-only flexible sigmoidoscopy screening can reduce colorectal cancer incidence and mortality, especially in men. While women experienced some reduction in cancer incidence, the effect on cancer death was not statistically significant.

The study supports the long-term value of endoscopic screening and highlights the importance of considering sex-specific differences when designing population screening programs. It also raises important questions about the optimal choice of screening method and how healthcare systems can best allocate resources for cancer prevention.

SEO Keywords

Colorectal cancer screening, sigmoidoscopy benefits, long-term cancer prevention, NORCCAP trial, colorectal cancer mortality reduction, cancer screening UK, preventive gastroenterology, endoscopic screening effectiveness

Sources

• Botteri E, Holme Ø, Løberg M, et al. Twenty-Three–Year Benefits of Sigmoidoscopy Screening for Colorectal Cancer: A Randomized Trial. Annals of Internal Medicine, 2026
• American College of Physicians (ACP) Journals, Annals of Internal Medicine publication page
• NORCCAP (Norwegian Colorectal Cancer Prevention) trial data and follow-up registry analysis

Disclaimer

This article is a rewritten, simplified summary created for educational and informational SEO purposes. It does not replace professional medical advice, diagnosis, or treatment. Readers should consult qualified healthcare professionals for medical guidance related to colorectal cancer screening or any health condition.