Risk of extra-intestinal cancer in inflammatory bowel disease: meta-analysis of population-based cohort studies

Extra-intestinal manifestations of inflammatory bowel disease (IBD) are relatively common, whereas the risk of extra-intestinal cancer (EIC) remains uncertain. The aim of this study was to obtain a reliable estimate of the risk of EIC in Crohn's disease (CD) and ulcerative colitis (UC) by performing a meta-analysis of population-based cohort studies.

A systematic literature review was performed using MEDLINE (1966-2009) and abstracts from recent international conferences. Eight population-based cohort studies comprising a total of 17,052 patients with IBD were available. Standardized incidence ratios (SIRs) of EICs were pooled in a meta-analysis approach using STATA software.

Overall, IBD patients were not at increased risk of EIC (SIR, 1.10; 95% confidence interval (CI) 0.96-1.27). However, site-specific analyses revealed that CD patients had an increased risk of cancer of the upper gastrointestinal tract (SIR 2.87, 95% CI 1.66-4.96), lung (SIR 1.82, 95% CI 1.18-2.81), urinary bladder (SIR 2.03, 95% CI 1.14-3.63), and skin (SIR 2.35, 95% CI 1.43-3.86). Patients with UC had a significantly increased risk of liver-biliary cancer (SIR 2.58, 95% CI 1.58-4.22) and leukemia (SIR 2.00, 95% CI 1.31-3.06) but a decreased risk of pulmonary cancer (SIR 0.39, 95% CI 0.20-0.74).

Although the overall risk of EIC was not significantly increased among patients with IBD, the risk of individual cancer types differed from that of the background population as well as between CD and UC patients. These findings may primarily be explained by smoking habits, extra-intestinal manifestations of IBD, and involvement of the upper gastrointestinal tract in CD.