In IBD, multiple affected relatives — not early-onset family history — added the most colorectal cancer risk

Design

Nationwide register-based matched cohort, Sweden, 1996–2023

Population

124,387 people with IBD and 1,213,641 matched comparators

Primary outcome

Colorectal cancer incidence by family history

Effect

≥2 affected relatives: +2.69 (95% CI 0.60–4.78) per 1,000 person-years; early-onset: +0.42 (−0.47 to 1.31)

This Swedish nationwide register cohort (1996–2023) followed 124,387 people with IBD and 1.2 million matched comparators for a median of 11 years, classifying family history by the number of first-degree relatives with colorectal cancer and their age at diagnosis.

Colorectal cancer incidence was 1.17 per 1,000 person-years in IBD versus 0.88 in comparators. In IBD, two or more affected relatives added 2.69 extra cases per 1,000 person-years (95% CI 0.60–4.78); a relative diagnosed before 50 added only 0.42 (−0.47 to 1.31). On the absolute scale, family history raised risk similarly in IBD and comparators; its relative effect was smaller in IBD because baseline risk was already higher.

Guidelines single out a first-degree relative with early-onset colorectal cancer as a reason for annual surveillance colonoscopy in IBD. These data suggest the number of affected relatives may matter more. They are observational and do not by themselves justify changing surveillance intervals, but they sharpen the family history clinicians take.

• Record the number of first-degree relatives with colorectal cancer, not only whether any relative was under 50.
• Treat two or more affected relatives as a strong reason for intensified surveillance in IBD.
• Continue colitis surveillance according to extent, duration and inflammation activity.
• Update family history at each review; it changes over time.

Why it matters

It challenges the guideline emphasis on early-onset family history as the key hereditary trigger for closer surveillance.

Don't overread it

Observational register data; the early-onset estimate is imprecise and the study does not test surveillance strategies.

The statistics, in plain English

An extra 2.69 cases per 1,000 person-years means about 27 extra cancers per 1,000 patients followed for 10 years — but the interval (0.60–4.78) is wide.

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