BACKGROUND & AIMS: Treatment with immunosuppressive thiopurines such as azathioprine is associated with an increased risk of leukemogenesis. We assessed the risk of myeloid disorders, such as acute myeloid leukemia and myelodysplastic syndromes, in a large cohort of patients with inflammatory bowel disease (IBD) in France.

METHODS

We performed a prospective observational study of 19,486 patients with IBD enrolled in the Cancers Et Surrisque Associé aux Maladies inflammatoires intestinales En France (CESAME) study from May 2004 through June 2005; patients were followed through December 31, 2007. The incidence of myeloid disorders in the general population, which was used for reference, was determined from the French Network of Cancer Registries.

RESULTS

During 49,736 patient-years of follow-up, 5 patients were diagnosed with incident myeloid disorders (2 with acute myeloid leukemia and 3 with myelodysplastic syndromes). Four of these patients had been exposed to thiopurines (1 with ongoing treatment and 3 with past exposure). The risk of myeloid disorders was not increased among the overall IBD population, compared with the general population; the standardized incidence ratio (SIR) was 1.80 (95% confidence interval [CI], 0.58-4.20). The risk of myeloid disorders was not increased among patients with IBD and ongoing thiopurine treatment (SIR, 1.54; 95% CI, 0.05-8.54), but patients with past exposures to thiopurines had an increased risk of myeloid disorders (SIR, 6.98; 95% CI, 1.44-20.36).

CONCLUSIONS

Past exposure to thiopurines increases the risk of myeloid disorders 7-fold among patients with IBD. This finding should be considered when initiating thiopurine therapy, so risks and benefits can be calculated.