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Risk of Extra-Intestinal Cancer in IBD Elucidated

Am J Gastroenterol 2010.

Patients with Crohn's disease (CD) have a slightly higher risk of extra-intestinal cancer as compared to a matched background population, a new meta-analysis shows.

"This increased risk is likely to be explained by disease involvement of the upper GI tract, extra-intestinal manifestations of the disease, and smoking habits," senior author Dr. Tine Jess of Copenhagen University Hospital in Denmark told Reuters Health by email.

Patients with ulcerative colitis (UC), on the other hand, do not have a higher overall risk for extra-intestinal cancer. "However, the pattern is somewhat different from that of the background population, as UC patients have an increased risk of liver-biliary cancers (probably due to primary sclerosing cholangitis) counterweighted by a decreased risk of pulmonary cancer (probably due to the low prevalence of smokers among UC patients)," Dr. Jess said.

The findings stem from a systematic review and meta-analysis of eight population-based cohort studies comprising a total of 17,052 patients with inflammatory bowel disease (IBD).

In a March 23 advance online publication of the American Journal of Gastroenterology, the investigators explain that they included only studies that reported the total number of patients followed, the expected and exact numbers of extra-intestinal cancers in the cohort during follow up, and/or rates of observed to expected extra-intestinal cancer cases with 95% confidence intervals.

In comments to Reuters Health, Dr. Jess further explained that the meta-analysis "did not provide crude estimates of 'how common' extra-intestinal cancers in IBD patients are, but a comparison of occurrence among IBD patients as compared to the background population (where time of observation is taken into account)."

Overall, IBD patients were not at increased risk of extra-intestinal cancer; the standardized incidence ratio (SIR) was 1.10. However, analysis of individual cancer types revealed that CD patients had an increased risk of cancer of the upper GI tract (SIR 2.87), lung (SIR 1.82), urinary bladder (SIR 2.03), and skin (squamous; SIR 2.35).

Four population-based studies showed that patients with UC had a significantly decreased risk of lung cancer (SIR 0.39) and overall cancer of the respiratory tract (SIR 0.67) compared with the background population, but a significantly increased risk of liver-biliary cancer (SIR 2.58) and leukemia (SIR 2.00). Data on UC patients also showed a trend toward increased risk of squamous cell carcinoma (SIR 1.68).

While extra-intestinal manifestations of IBD are relatively common, occurring in upwards of 35% of patients, the risk of extra-intestinal cancer has been unclear until now, the authors say.

The present results, they note, likely provide a "fairly valid and generalizable picture of the occurrence of extra-intestinal cancer in IBD and suggest a causal role of extra-intestinal manifestations of disease as well as of smoking."