In IBD, count the affected relatives rather than their age

Design

nationwide register-based matched cohort study, 1996–2023, median 11 years' follow-up

Population

124,387 patients with inflammatory bowel disease and 1,213,641 matched general-population comparators, Sweden

Primary outcome

colorectal cancer incidence rate and rate difference by family history

Effect

IBD 1.17 vs comparators 0.88 per 1,000 person-years; ≥2 affected relatives +2.69 (95% CI 0.60–4.78); early-onset relative +0.42 (−0.47–1.31)

Surveillance guidance in inflammatory bowel disease singles out patients with a family history of early-onset colorectal cancer. This nationwide Swedish register study, covering 1996 to 2023, asked whether that is where the risk actually sits. It followed 124,387 patients with inflammatory bowel disease and 1,213,641 general-population comparators matched for age, sex, parish and year, for a median 11 years, classifying family history by the number of affected first-degree relatives and their age at diagnosis.

Colorectal cancer occurred at 1.17 per 1,000 person-years in the inflammatory bowel disease cohort (1,882 events) against 0.88 in comparators (14,177 events). Within the disease cohort, the largest absolute increase came with two or more affected relatives: 2.69 additional cases per 1,000 person-years (95% CI 0.60 to 4.78) against no family history. Early-onset colorectal cancer in a relative added much less: 0.42 additional cases per 1,000 person-years (−0.47 to 1.31), an interval that includes no effect at all.

Incidence rates were otherwise similar between patients and matched comparators with the same family history — the excess attributable to inflammatory bowel disease itself was concentrated in those with no family history, where baseline risk was already raised. Because that baseline is higher, the relative effect of family history looks weaker in inflammatory bowel disease even though the absolute effect is the same. The authors draw the obvious conclusion and put it as a question: surveillance strategies may be prioritising the wrong branch of the family history.

• Record the number of affected first-degree relatives, not only whether any had early-onset disease
• Treat two or more affected relatives as the strongest family-history signal for surveillance intensity
• Do not downgrade surveillance in a patient with no family history — their excess risk comes from the disease
• Re-ask the family history periodically; relatives are diagnosed after the patient is

Why it matters

Guidelines flag the family history feature with the weaker evidence behind it.

Don't overread it

This is observational register data raising a question about guideline emphasis, not a trial of two surveillance strategies.

The statistics, in plain English

These are absolute rate differences per 1,000 person-years, which is the right scale for a surveillance decision: 2.69 extra cases per 1,000 person-years is roughly one extra cancer for every 370 patients followed a year. The early-onset interval of −0.47 to 1.31 includes zero, so that effect is not established rather than shown to be absent. Register data capture diagnoses, not the reason surveillance was or was not done, so patients with a known family history may already have been scoped more often — which would if anything understate their risk.

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