The first randomised trial of colonoscopy screening: what NordICC actually showed
Inviting people to a single colonoscopy cut 10-year colorectal cancer risk from 1.20% to 0.98%. The reduction in cancer deaths did not reach significance — and only 42% of those invited turned up.
| Group | Value (%) |
|---|---|
| Invited to colonoscopy | 0.98 |
| Usual care | 1.2 |
Colonoscopy is treated as the gold standard of bowel-cancer screening, yet until 2022 no randomised trial had ever tested whether inviting people to one actually reduces their risk of colorectal cancer or death. The NordICC trial finally did — and its result was more modest than the procedure's reputation. Inviting people to a single colonoscopy lowered their 10-year risk of colorectal cancer, but the reduction in cancer deaths did not reach statistical significance, and the effect was blunted by the fact that fewer than half of those invited attended.
What the trial did
NordICC, published in the New England Journal of Medicine, drew presumptively healthy men and women aged 55 to 64 from population registries in Poland, Norway, Sweden and the Netherlands [s1]. Participants were randomly assigned in a 1:2 ratio either to receive an invitation to a single screening colonoscopy or to receive no invitation and no screening — usual care [s1]. Follow-up data were available for 84,585 people: 28,220 in the invited group and 56,365 in the usual-care group [s1].
One number frames everything that follows. Of the 28,220 people invited, only 11,843 — 42.0% — actually underwent the colonoscopy [s1]. That is the reality of screening programmes, and NordICC's main analysis was deliberately designed to reflect it.
The headline result
The trial reported two ways of looking at the data. The primary, most rigorous analysis is intention-to-screen: it compares everyone invited with everyone in usual care, whether or not they showed up. On that basis, over a median follow-up of 10 years, the risk of colorectal cancer was 0.98% in the invited group versus 1.20% in the usual-care group — a relative reduction of 18% (risk ratio 0.82, 95% confidence interval 0.70 to 0.93) [s1].
The risk of dying from colorectal cancer was 0.28% in the invited group and 0.31% in usual care, a difference that did not reach statistical significance (risk ratio 0.90, 95% confidence interval 0.64 to 1.16) [s1]. Death from any cause was essentially identical: 11.03% versus 11.04% [s1]. To prevent a single case of colorectal cancer, 455 people had to be invited to screening (95% confidence interval 270 to 1,429) [s1].
Why the effect looks smaller than expected
The disappointment many readers felt at these numbers comes largely from the 42% attendance figure. Because more than half the invited group never had the procedure, the intention-to-screen result measures the effect of offering colonoscopy to a population, not the effect of having one. When the trial modelled what would have happened if everyone invited had attended, the estimated benefit was larger — but that adjusted figure is a modelled estimate, more vulnerable to assumptions than the primary result, and the trial's authors kept intention-to-screen as the headline for good reason.
On safety, the trial was reassuring: there were 15 cases of major bleeding after polyp removal, and no perforations or screening-related deaths within 30 days of colonoscopy [s1]. These are the harms any screening decision has to weigh against the benefits, and here they were uncommon.
How it fits the wider guidance
NordICC does not overturn the case for bowel-cancer screening, and it was never a comparison of colonoscopy against other tests such as stool-based screening. It is one randomised trial of one strategy — a single invitation — with longer-term follow-up still to come.
The broader guidance rests on modelling as well as trials. The US Preventive Services Task Force recommends screening for colorectal cancer in all adults aged 50 to 75, with high certainty of substantial net benefit, and in 2021 extended a recommendation to adults aged 45 to 49, with moderate certainty of moderate net benefit [s2]. That extension reflects a documented shift in the disease: an estimated 10.5% of new colorectal cancers now occur in people younger than 50, and incidence in adults aged 40 to 49 rose by almost 15% between 2000–2002 and 2014–2016 [s2]. The Task Force also notes how much screening is missed — 26% of eligible US adults had never been screened as of 2016 [s2].
The honest summary is that colonoscopy screening reduces colorectal cancer risk, that the size of the benefit in a real population depends heavily on how many people attend, and that its effect on cancer deaths, in the first randomised trial, was in the right direction but not statistically proven at 10 years [s1]. This article is informational and is not medical advice; whether and how to be screened is a decision for an individual and their clinician.
Sources
- [s1] Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death — New England Journal of Medicine, 27 October 2022. https://doi.org/10.1056/NEJMoa2208375
- [s2] Screening for Colorectal Cancer: US Preventive Services Task Force Recommendation Statement — JAMA, 18 May 2021. https://doi.org/10.1001/jama.2021.6238
Sources
- Effect of Colonoscopy Screening on Risks of Colorectal Cancer and Related Death — New England Journal of Medicine , October 27, 2022
- Screening for Colorectal Cancer: US Preventive Services Task Force Recommendation Statement — JAMA , May 18, 2021
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