Children who develop inflammatory bowel disease run a higher risk of cancer, both in childhood and later in life, a study from Karolinska Institutet published in The BMJ journal reports.

Adulthood onset inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease have been associated with an increased risk of bowel cancer. However, there have been no studies showing how the cancer risk is affected by childhood onset of the disease and whether it changes over time.

Using data from the Swedish National Patient Register, researchers at Karolinska Institutet have now compared the incidence of cancer in 9,405 individuals who were diagnosed with inflammatory bowel disease as children, with 92,870 individuals from the general population.

Their results show that individuals who developed inflammatory bowel disease before the age of 18 had twice the cancer risk during childhood and adolescence as well as adulthood, compared with people who did not have such a diagnosis. The largest increase in risk was observed for bowel cancer, but there was also an increase in risk for other forms of cancer, such as blood and skin cancers. “We believe that the main cause is the chronic inflammation, which we know to be a driving factor for many different cancer types,” said principal investigator Ola Olén at Karolinska Institutet’s Clinical Epidemiology Unit at the Department of Medicine, Solna. “Early onset means that the body is exposed to inflammation for a longer time.”

The study participants were diagnosed with inflammatory bowel disease between 1964 and 2014.

“The treatment for inflammatory bowel disease improved considerably over these years, thanks in part to the introduction of new immunomodulating drugs, but unfortunately we can’t see that the relative incidence of cancer simultaneously declined,” said Dr Olén.

Adult patients with inflammatory bowel disease are regularly invited to colonoscopy screenings, which can detect the presence of any cancer in the gut. The researchers believe that the knowledge of the cancer risk associated with the early onset of inflammatory bowel disease has to be factored into decisions on colonoscopy screening for children and adolescents, from both a healthcare and a patient perspective.”

“Don’t forget that even if relative risks are high, the absolute risks are much more modest, and during childhood absolute risks are extremely small. Most young people don’t get cancer, and some of these forms of tumours are extremely rare,” explained Dr Olén. “But it’s probably important for individuals who develop inflammatory bowel disease in childhood to make sure to attend the examinations they’re invited to, especially those who have other strong risk factors for cancer, such as a family history of early cancer.”