One-time sigmoidoscopy lowers long-term cancer risk
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).

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.