Does CRC Risk in IBD Extend to Close Family Members?

Megan Brooks

March 01, 2023

The risk of colorectal cancer (CRC) among patients with inflammatory bowel disease (IBD) does not extend to close family members, new research suggests.

In a large Swedish study, a history of IBD among first-degree relatives was not associated with an increased risk of CRC, even when considering various characteristics of IBD and CRC history.

The findings suggest that extra screening for CRC may not be needed for children, siblings, or parents of those with IBD, say the study authors, led by Kai Wang, MD, PhD, with Harvard T. H. Chan School of Public Health, Boston. The findings strengthen the theory that it's inflammation or atypia of the colon of people with IBD that confers the increased CRC risk.

"There is nothing in this study that changes our existing practice," said Ashwin Ananthakrishnan, MD, MPH, with Massachusetts General Hospital and Harvard Medical School in Boston, who was not involved in the research. "It is already the thought that inflammation in IBD increases risk of cancer," which would not increase CRC risk among family members.

The study appeared in the International Journal of Cancer.

Patients with IBD are known to be at increased risk for CRC. However, the association between family history of IBD and CRC risk remains less clear. Current CRC screening recommendations are the same for patients who have family members with IBD and for those who do not.

The Swedish nationwide case-control study included 69,659 individuals with CRC, of whom 1599 (2.3%) had IBD, and 343,032 matched control persons who did not CRC, of whom 1477 (0.4%) had IBD.

Overall, 2.2% of CRC case patients and control patients had at least one first-degree relative who had a history of IBD.

After adjusting for family history of CRC, the authors did not find an increase in risk for CRC among first-degree relatives of people with IBD (odds ratio, 0.96; 95% CI, 0.91 – 1.02).

The null association was consistently observed regardless of IBD subtype (Crohn's disease or ulcerative colitis), the number of first-degree relatives with IBD, age at first IBD diagnosis, maximum location or extent of IBD, or type of relative (parent, sibling, or offspring). The null association remained for early-onset CRC diagnosed before age 50.

Overall, these findings suggest that IBD and CRC may not have substantial familial clustering or shared genetic susceptibility and provide "robust evidence that a family history of IBD did not increase the risk of CRC, supporting use of the same routine CRC screening strategy in offspring, siblings and parents of IBD patients as in the general population," Wang and colleagues conclude.

This "well-done" study is one of the largest to date to evaluate first-degree relatives of IBD patients and their risk of CRC, said Shannon Chang, MD, with NYU Langone Health Inflammatory Bowel Disease Center, who wasn't involved in the research.

The findings are reassuring, as the authors assessed several factors and found that family members of patients with IBD are not at higher risk for CRC compared with the general population, Chang added.

Support for the study was provided by the National Institutes of Health, the American Cancer Society, ALF funding, the Swedish Research Council, and the Swedish Cancer Foundation. Wang, Chang and Ananthakrishnan have disclosed no relevant financial relationships.

Int J Cancer. Published online February 9, 2023. Abstract

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