Risk of malignancies in patients with inflammatory bowel disease who used thiopurines as compared with other indications: a territory-wide study

AIMS: Thiopurines are believed to increase cancer risks, but data from Asian patients are sparse. We determined the risks of malignancies in thiopurine users with inflammatory bowel disease (IBD) or other indications from Hong Kong. METHODS: All patients who had received thiopurines between 2005 and 2009 in Hong Kong were identified from local electronic healthcare database. Patients were followed from the start date of thiopurines until death or end of study in 2017. We excluded patients with baseline malignancy. Standardized incidence ratios (SIR) and the corresponding 95% confidence intervals (CI) of all malignancies were computed against matched local general population from the cancer registry. Patients in the same diagnosis category but not exposed to thiopurines were included as controls. RESULTS: There were 7452 thiopurines users (median age 47.0 years), including 595 IBD patients, with a median follow-up of 11.2 years. Of them, 684 (9.2%) developed malignancies with an overall SIR of 2.30 (95% CI 2.13–2.48). The SIR in IBD patients who used thiopurines was 2.37 (95% CI 1.71–3.18) as compared with non-users (SIR 1.35, 95% CI 1.05–1.72). Highest risk of malignancies was observed in post-transplant patients (SIR 3.83, 95% CI 3.34–4.35), and lower risks were seen in patients with rheumatological diseases (SIR 1.46, 95% CI 1.02–2.02). CONCLUSION: IBD patients in Hong Kong who used thiopurines had 2.37-fold increase in risk of malignancies than the general population, which was higher than non-users and different from thiopurine users for other indications.