Excess risk of urinary tract cancers in patients receiving thiopurines for inflammatory bowel disease: a prospective observational cohort study

{Background The risk of urinary tract cancers, including kidney and bladder cancers, was increased in transplant recipients receiving thiopurines. Aim To assess the risk of urinary tract cancers in patients with inflammatory bowel disease (IBD) receiving thiopurines in the CESAME observational cohort. Methods Between May 2004 and June 2005, 19 486 patients with IBD, 30.1% of whom were receiving thiopurines, were enrolled. Median follow-up was 35 months (IQR: 29-40). Results Ten and six patients developed respectively kidney and bladder cancer. The incidence rates of urinary tract cancer were 0.48/1000 patient-years in patients receiving thiopurines (95% CI: 0.21-0.95), 0.10/1000 patient-years in patients who discontinued thiopurines (95% CI: 0.00-0.56) and 0.30/1000 patient-years in patients never treated with thiopurines (95% CI: 0.12-0.62) at entry. The standardised incidence ratio of urinary tract cancer was 3.40 (95% CI: 1.47-6.71