Objectives: The objective of this study was to assess inflammatory bowel disease (IBD) medications in relation to lymphoma risk. Methods: Information on IBD and relevant medications and other utilization was obtained from the Kaiser Permanente IBD Registry, 1996-2009. Lymphoma cases were ascertained from the Kaiser Permanente Cancer Registry. Lymphoma incidence was compared between the IBD cohort and the general Kaiser Permanente population. Results: Of the 16,023 IBD patients without human immunodeficiency virus followed an average 5.8 years, 43 developed lymphoma. IBD patients with and without lymphoma did not differ with respect to past IBD-related visits, procedures, or tests. The standardized incidence rate ratio (SIRR) for lymphoma among IBD patients with no dispensing of thiopurine or anti-tumor necrosis factor (TNF) was 1.0 (95% confidence interval (CI): 0.96-1.1). Of the 21,282 person-years involving exposure to thiopurine or anti-TNF, 81% involved thiopurine alone; 3%, anti-TNF alone; and 16%, combination therapy. Among patients with thiopurine but not anti-TNF dispensings, the SIRR was 0.3 (95% CI: 0.2-0.4) for past use and 1.4 for current use (95% CI: 1.2-2.7). Among patients with dispensing of anti-TNF (with and without thiopurine), the SIRR was 5.5 for past use (95% CI: 4.5-6.6) and 4.4 for current use (95% CI: 3.4-5.4). The most common lymphoma subtypes were diffuse large B-cell lymphoma (44%), follicular lymphoma (14%), and Hodgkin's disease (12%). Conclusions: Our study provides evidence that IBD alone is not associated with the risk of lymphoma. Use of anti-TNF with thiopurine and current use of thiopurine alone were associated with increased risk, although the effect of disease severity merits further evaluation.
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