NordICC: inviting people to a screening colonoscopy reduced bowel cancer, but less than expected
The first randomised trial of colonoscopy screening found an 18% reduction in bowel cancer incidence after 10 years among those invited, with no significant reduction in bowel cancer deaths; only 42% of invitees actually had the procedure.
NordICC randomised 84,585 people aged 55-64 in Poland, Norway and Sweden to an invitation to a single screening colonoscopy or to usual care with no screening. The primary endpoints were colorectal cancer incidence and death at 10 years, analysed by intention to screen.
The 10-year risk of colorectal cancer was 0.98% in the invited group and 1.20% in usual care (risk ratio 0.82). Colorectal cancer death was 0.28% versus 0.31%, not significantly different. In the adjusted per-protocol analysis, assuming everyone invited had attended, incidence fell 31% and death 50%.
The trial prompted a wide debate about the real-world effect of colonoscopy programmes versus stool-test programmes.
- Colorectal cancer incidence at 10 years: 0.98% vs 1.20% (RR 0.82, 95% CI 0.70-0.93) by intention to screen
- Colorectal cancer death: 0.28% vs 0.31% (RR 0.90, 95% CI 0.64-1.16)
- Only 42% of those invited underwent colonoscopy
- Adjusted per-protocol estimate: incidence RR 0.69, death RR 0.50 among those who attended
- Number needed to invite to prevent one cancer over 10 years: 455
A colonoscopy probably does reduce bowel cancer risk for the person who has it, but a programme that offers colonoscopy achieves much less if most people decline. Programmes based on stool tests with high uptake may deliver as much population benefit at lower cost and risk.
- Low participation dilutes the intention-to-screen effect; the per-protocol estimate relies on modelling assumptions
- Ten years is short for a mortality endpoint after polyp removal; a 15-year analysis is planned
- Adenoma detection rates varied between endoscopists and some were below quality thresholds
- Results apply to a one-off colonoscopy at 55-64, not to repeated colonoscopy programmes as practised in the US
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