Design: randomised noninferiority trial across eight European countries, interim analysis at 5.5 years (EPoS II)
Population: 10,799 patients after removal of high-risk adenomas (>=10 mm, high-grade dysplasia, villous growth, or 3-10 adenomas)
Primary outcome: cumulative incidence of colorectal cancer (10 years at final analysis; 5 years reported here)
Effect: 0.77% with first surveillance at 5 years vs 0.82% at 3 years; difference -0.05 percentage points, upper boundary of the 99.12% CI 0.68 against a 0.7-point margin

EPoS II randomised 10,799 patients across eight European countries who had had high-risk adenomas removed — an adenoma 10 mm or larger, with high-grade dysplasia or villous growth, or three to ten adenomas of any kind — to a first surveillance colonoscopy at five years or at three years. Three years is what current guidelines recommend.

At the interim analysis after 5.5 years, cumulative colorectal cancer incidence at five years was 0.77% in the five-year group and 0.82% in the three-year group. The difference of -0.05 percentage points met the prespecified noninferiority criterion. Cancer stage at diagnosis did not appear to differ substantially, and five patients in total died of colorectal cancer across both arms.

The practical weight of this is in endoscopy capacity. Surveillance after polypectomy consumes a large and growing share of colonoscopy lists, and in systems where the waiting time for a diagnostic colonoscopy in a symptomatic patient runs to months, a two-year extension of the surveillance interval for a well-defined group frees exactly the capacity that is scarce. That argument applies with particular force in Indian public-sector endoscopy units.

Two cautions. This is an interim report of a trial whose primary endpoint is cancer incidence at ten years, and it is the five-year comparison that has been met. And the three-year group also had a colonoscopy at five years, so the comparison is five-year-only surveillance against surveillance at both three and five.

Discuss a five-year first surveillance interval with patients who meet the trial's high-risk adenoma definition
Check the definition applies: adenoma 10 mm or more, high-grade dysplasia, villous growth, or three to ten adenomas
Do not extend the interval for patients outside that definition — more than ten adenomas or a syndrome is a different pathway
Where guidelines still specify three years, document the discussion rather than changing practice silently
Use the released capacity for symptomatic diagnostic lists, which is where the benefit of this result actually lands

Don't overread it

This is an interim analysis reporting cancer incidence at five years; the trial's actual primary endpoint is incidence at ten years and has not been reached.

The statistics, in plain English

The noninferiority margin was 0.7 percentage points on the upper boundary of the confidence interval for the difference in cancer incidence; the observed upper boundary was 0.68, so the criterion was met — but only just. That narrowness matters because this is a one-sided 99.12% interval used at interim analysis, deliberately conservative to protect the overall error rate, and the final 10-year analysis will use a 95.33% interval. Inverse probability weighting was used to handle patients who did not attend their five-year colonoscopy, which is a statistical correction for missing data rather than observed data.