Risk of lymphoma in inflammatory bowel disease.

OBJECTIVE: Inflammatory bowel disease with a subsequent diagnosis of non-Hodgkin's lymphoma has been reported. There is concern that the risk of developing lymphoma will rise with increasing use of immune modifier therapy. We determined the risk of non-Hodgkin's lymphoma in an U.S. population-based inception cohort, and evaluated the association between inflammatory bowel disease and lymphoma in our referral practice.
METHODS: The records of all incidence cases of inflammatory bowel disease in Olmsted County, Minnesota, between 1950 and 1993 were reviewed for the diagnosis of lymphoma. Standardized incidence ratios (observed/expected) were used to estimate relative risk. In addition, the clinical features and outcomes of all patients with inflammatory bowel disease and lymphoma seen at Mayo Clinic between 1976 and 1997 were reviewed.
RESULTS: Among 454 county residents diagnosed with inflammatory bowel disease, a single non-Hodgkin's lymphoma occurred in a patient with Crohn's disease. No cases were seen with ulcerative colitis. The estimated relative risk of lymphoma was 2.4 in Crohn's disease (95% confidence interval, 0.1-13), 0 in ulcerative colitis (0-6), and 1.0 in inflammatory bowel disease overall (0.03-6). Between 1976 and June 1997, 61 patients with inflammatory bowel disease and lymphoma (approximately 0.41%) were seen in the referral practice. In four patients with Crohn's disease (13%), potential neoplastic risk factors were identified-therapeutic radiation in 1, and use of purine analogs in 3 (median length of use, 11 months).
CONCLUSIONS: Our population-based cohort study demonstrated that the absolute risk of non-Hodgkin's lymphoma remains quite small (0.01% per person-year). This risk may not exceed that in the general population. In our referral practice, immune modifier therapy could be potentially implicated in only 5% of cases of lymphoma occurring in the setting of inflammatory bowel disease.