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Cancer incidence among patients with ankylosing spondylitis in Sweden 1965–95: a population based cohort study

Background: Ankylosing spondylitis (AS) is a chronic inflammatory joint disease which may lead to extra-articular complications. The disease associated cancer risk has been poorly explored. Recently, tumour necrosis factor α blockers have been found to be efficacious in AS, but their long term risk is unknown. Objective: To analyse a large national cohort of patients with AS to determine the overall cancer risk in AS as a background to the future introduction of new treatments. Methods: All patients with AS admitted to Swedish hospitals 1965–95 were linked through individual national registration numbers to the Swedish Cancer Register and National Death Register. Standardised incidence ratio (SIR) of cancer risk was calculated in 6621 people, monitored during 67 885 person-years. Results: No overall increase in cancer risk was found (SIR 1.05, 95% CI 0.94 to 1.17). Rectal cancer was less common (SIR 0.41, 95% CI 0.15 to 0.89) while unspecified kidney cancer was more common (SIR 5.90, 95% CI 1.61 to 15.1). Risks for colon, renal parenchymal, and renal pelvic cancer were not significantly increased. Laryngeal cancer was more common than expected, while lung cancer was not. Risks of haematopoietic malignancies were not increased. Conclusions: No overall increase in cancer risk was found. The decreased risk of rectal cancer might be due to local application of NSAIDs, and the increased risk of unspecified kidney cancer to frequent radiological pelvic examinations. If information on disease characteristics, including HLA-B27, was available for individual patients with cancer, risk-benefit analysis of long term effects of new immunomodulation treatment might be improved.