Risk of cancer in patients with ankylosing spondylitis: a nationwide cohort study in Taiwan.

Objective: To estimate the incidence of cancer among patients with ankylosing spondylitis (AS) and compare this risk with that of the general population.Method: We obtained data from Taiwan's National Health Insurance database on 19 289 patients with a first diagnosis of AS registered between 2000 and 2012 with no history of cancer before the diagnosis of AS. Standardized incidence ratios (SIRs) for all cancers and for site-specific cancers were used to assess whether AS was associated with an increased risk of cancer.Results: During the follow-up period, 485 patients developed cancer. The incidence rate was therefore 256.3 per 100 000 person-years. Compared with the general population, patients with AS had an increased risk of cancer [SIR 1.33, 95% confidence interval (CI) 1.20-1.47]. The SIR of cancer was higher in older patients; the risk increased from 8 years after initial diagnosis. Among solid tumours, the risk of melanoma was the highest (SIR 4.64, 95% CI 1.93-11.15), followed by prostate (SIR 2.53, 95% CI 2.01-3.19), thyroid (SIR 2.09, 95% CI 1.45-3.00), and bone cancer (SIR 2.00, 95% CI 1.01-3.99). Among haematological cancers, the risk of leukaemia was the highest (SIR 1.94, 95% CI 1.21-3.12). By contrast, the risks of oesophageal and oral cancers decreased in patients with AS.Conclusion: This nationwide population-based cohort study demonstrated that patients with AS in Taiwan are at an increased risk of cancer, particularly melanoma; prostate, thyroid, and bone cancers; and haematological malignancies.