Twenty-Three Year Benefits of Sigmoidoscopy Screening for Colorectal Cancer: A Randomized Trial
Inviting adults to a one-time lower-colon scope exam reduced colorectal cancer risk for 23 years, with fewer colorectal cancer deaths only in men.
*Randomized controlled trial; Level 1b (OCEBM).
*Randomized controlled trial; Level 1b (OCEBM).
Citation
Botteri E, Holme Ø, Løberg M, Bretthauer M, Kalager M, Randel KR, Hoff G. Twenty-Three Year Benefits of Sigmoidoscopy Screening for Colorectal Cancer: A Randomized Trial. Annals of Internal Medicine. 2026;179:804-811. doi:10.7326/ANNALS-25-05456.
Background
Prior trials show sigmoidoscopy screening lowers colorectal cancer risk for up to 15 years, but longer-term benefits and differences between men and women were uncertain. This population-based Norwegian trial assessed outcomes after 23 years.
Patients
People aged 50 to 64 years living in Oslo or Telemark County, Norway; excluded if they had known colorectal cancer at randomization.
Intervention
Invitation to one-time sigmoidoscopy (a scope exam of the lower colon), with or without a single stool blood test; follow-up colonoscopy if findings were abnormal.
Control
Usual care (no screening invitation).
Outcome
Colorectal cancer incidence and death.
Follow-up Period
Up to 23 years (through December 2023).
Results
| Outcome at 23 years | Absolute risk (screening vs no screening) | Absolute risk difference | Number needed to invite (NNT) |
|---|---|---|---|
| Colorectal cancer incidence (men) (primary) | 4.3% vs 6.0% | -1.7% | 59 |
| Colorectal cancer incidence (women) (primary) | 4.2% vs 4.7% | -0.5% | 200 |
| Colorectal cancer death (men) (primary) | 1.4% vs 2.2% | -0.8% | 125 |
Analyses were intention-to-treat. Adding a single stool blood test to sigmoidoscopy did not improve benefits.
Limitations
Follow-up relied on national registries, and the trial tested only a one-time screening invitation; results may differ with repeated testing. The lack of colorectal cancer death reduction in women remains unexplained.
Funding
Norwegian government and Norwegian Cancer Society; funders had no role in the trial.
Clinical Application
For average-risk adults 50–64, one-time sigmoidoscopy can reduce long-term colorectal cancer risk; mortality benefit was shown only in men, so women may need different screening choices.
Discussion
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In this population-based randomized controlled trial of invitation to once-only sigmoidoscopy (± FIT) vs no screening, men had lower 23-year CRC death (1.4% vs 2.2%; risk difference −0.8%), but women did not (−0.1%). How should we judge validity and decide whether to change practice toward sex-specific screening strategies? Using the trial’s intention-to-treat results in men (CRC death 1.4% with screening invitation vs 2.2% with no screening at 23 years), what is the approximate number needed to invite for screening (NNT) to prevent one CRC death over 23 years?