Background & Aims: Earlier studies have provided varying risk estimates for lymphoma in patients with inflammatory bowel disease (IBD), but often have been limited by detection biases (especially during the first year of follow-up evaluation), misclassification, and small sample size; and rarely reflect modern-day management of IBD.

Methods: We performed a binational register-based cohort study (Sweden and Denmark) from 1969 to 2019. We compared 164,716 patients with IBD with 1,639,027 matched general population reference individuals. Cox regression estimated hazard ratios (HRs) for incident lymphoma by lymphoma subtype, excluding the first year of follow-up evaluation.

Results: From 1969 to 2019, 258 patients with Crohn's disease (CD), 479 patients with ulcerative colitis (UC), and 6675 matched reference individuals developed lymphoma. This corresponded to incidence rates of 35 (CD) and 34 (UC) per 100,000 person-years in IBD patients, compared with 28 and 33 per 100,000 person-years in their matched reference individuals. Although both CD (HR, 1.32; 95% CI, 1.16–1.50) and UC (HR, 1.09; 95% CI, 1.00–1.20) were associated with an increase in lymphoma, the 10-year cumulative incidence difference was low even in CD patients (0.08%; 95% CI, 0.02–0.13). HRs have increased in the past 2 decades, corresponding to increasing use of immunomodulators and biologics during the same time period. HRs were increased for aggressive B-cell non-Hodgkin lymphoma in CD and UC patients, and for T-cell non-Hodgkin lymphoma in CD patients. Although the highest HRs were observed in patients exposed to combination therapy (immunomodulators and biologics) or second-line biologics, we also found increased HRs in patients naïve to such drugs.

Conclusions: During the past 20 years, the risk of lymphomas have increased in CD, but not in UC, and were driven mainly by T-cell lymphomas and aggressive B-cell lymphomas.