Risk of malignant lymphomas in patients with inflammatory bowel disease: a population-based cohort study.

Objective: To estimate the risk of non-Hodgkin's lymphoma (NHL) and Hodgkin's lymphoma (HL) in patients with inflammatory bowel disease (IBD).

Design: We undertook a two-country population cohort study with all patients diagnosed with IBD in Norway and Sweden from 1987 and 1993 through 2015 and 2016, respectively, and analysed the risk of NHL and HL. In Sweden, we also analysed prescriptions of thiopurines and anti-tumour necrosis factor (TNF)-α therapy from 2005. We calculated standardised incidence ratios (SIRs) with 95% CIs using the general populations as reference.

Results: Among 131 492 patients with IBD with a medium follow-up of 9.6 years, we identified 369 cases of NHL and 44 cases of HL. The SIR of NHL was 1.3 (95% CI 1.1 to 1.5) in ulcerative colitis and 1.4 (95% CI 1.2 to 1.7) in Crohn's disease. We found no compelling heterogeneity in analyses stratified by patient characteristics. We found a similar pattern and magnitude of excess risks for HL. At 10 years, cumulative incidence was 0.26% (95% CI 0.23% to 0.30%) and 0.06% (95% CI 0.04% to 0.08%) for NHL and HL, respectively. Higher excess risks were found among patients with NHL with concomitant primary sclerosing cholangitis (SIR 3.4; 95% CI 2.1 to 5.2) and in those prescribed thiopurines alone (SIR 2.8; 95% CI 1.4 to 5.7) or with anti-TNF-α agents (SIR 5.7; 95% CI 2.7 to 11.9).

Conclusion: Patients with IBD have a statistically significant increased risk of malignant lymphomas compared with the general population, but the absolute risk remains low.