People with inflammatory bowel disease (IBD) already have a higher chance of developing bowel cancer than the general population. A large study from Sweden suggests that looking closely at how many close relatives have had bowel cancer, not just whether one relative was diagnosed young, could help doctors identify which patients face the greatest risk.
Background
IBD is a term used for long-term conditions that cause ongoing inflammation in the digestive system. The two main types are Crohn’s disease and ulcerative colitis, which can cause symptoms including stomach pain, diarrhoea, tiredness and bleeding from the bowel. Over time, ongoing inflammation in the colon can damage cells, which is one reason why bowel cancer risk is higher in people with IBD. Family history also plays a role in bowel cancer risk generally, because relatives can share inherited genes as well as lifestyle and environmental factors. Current guidance for people with IBD often focuses on whether a parent, sibling or child was diagnosed with bowel cancer before the age of fifty.
What the researchers found
Researchers at Karolinska Institutet in Sweden used national health records to study more than 124,000 people with IBD, comparing them with over 1.2 million people from the general population. Participants were followed for around eleven years on average, during which 1,882 people with IBD developed bowel cancer.
The researchers reported that the strongest warning sign was not necessarily a relative’s age at diagnosis, but the number of affected relatives. People with IBD who had two or more parents, siblings or children with bowel cancer were around two and a half times more likely to develop the disease themselves, compared with IBD patients with no family history. By comparison, having just one close relative diagnosed before the age of fifty was linked to a smaller increase in risk, of just under fifty per cent.
The team also examined absolute risk, meaning the real-world chance of developing bowel cancer rather than a comparison between groups. They found that people with a strong family history of bowel cancer had a broadly similar level of risk whether or not they also had IBD, suggesting family history itself carries substantial weight.
Why this matters
These findings suggest that counting how many relatives have had bowel cancer could become a useful addition to how doctors assess risk in people with IBD, alongside existing factors such as how long someone has had the condition, how much of the colon is affected and the level of inflammation present. The researchers said this detail is not currently a major focus of screening guidance, which tends to concentrate on a relative’s age at diagnosis.
What to keep in mind
This was an observational study, meaning it cannot prove that family history directly causes cancer in people with IBD. Shared genes, environment and lifestyle may all play a part. Not everyone with IBD and several affected relatives will develop bowel cancer. The study’s authors said further research is needed before screening guidelines are changed. Patients are not advised to alter their own screening schedule, but ensuring their healthcare team has an accurate and complete family cancer history may be worthwhile.
Reference
Song M, et al. Karolinska Institutet. Family history of colorectal cancer and risk of colorectal cancer in patients with inflammatory bowel disease. Gastroenterology. 2024. (Full author list, volume, page numbers and DOI were not available in the source material reviewed for this article.)
This article is a journalistic summary for informational purposes only. It does not constitute clinical advice or a recommendation to alter treatment decisions.