Long-term risk of malignancy after treatment of inflammatory bowel disease with azathioprine

Background: Data from renal transplant and rheumatoid arthritis patients suggest that there is an increased risk of malignancy after treatment with azathioprine. Whether this is true for patients with inflammatory bowel disease remains uncertain. Method: A retrospective review of clinical notes was performed. Results: Azathioprine was given to 626 of 2204 patients (855 with Crohn's disease and 1349 with ulcerative colitis). The mean total duration of azathioprine use was 27 months. The mean follow-up from diagnosis was 13.7 years and the mean follow-up from the start of azathioprine treatment was 6.9 years. Thirty-one cancers were observed in 30 patients treated with azathioprine (4.5%) and 77 cancers were observed in 70 patients not treated with azathioprine (4.5%; P=N.S.). Logistic regression analysis (including in the model the age, sex, diagnosis and extent of disease) showed that treatment with azathioprine did not significantly affect the risk of the development of cancer. Eight patients had lymphoma; three had been given azathioprine (P =N.S.). For patients with ulcerative colitis, the number of colorectal cancers (including high-grade dysplasia) in patients given azathioprine was eight of 355 (2.2%), compared with 28 of 994 (2.8%) for patients not given azathioprine (P =N.S.). The cumulative risk of colorectal cancer or dysplasia/dysplasia-associated lesion or mass (adjusted to exclude post-colectomy patients) after 10, 20, 30 and 40 years ofulcerative colitis was 0.4%, 1.3%, 9%and 15.5%, respectively. Conclusion: No increased risk of cancer diagnosis following azathioprine treatment was observed.