Increased Risk of Skin Cancer in Myasthenia Patients Treated with Azathioprine: A Nationwide Case-Control Study in Denmark (P02.192)

OBJECTIVE: To evaluate the association between use of azathioprine and risk of non-melanoma skin cancer (NMSC) in myasthenia gravis (MG) patients in a nationwide setting. BACKGROUND: Treatment of autoimmune MG frequently involves long-term exposure to immunosuppressants, including azathioprine. Use of azathioprine increases the risk of NMSC in organ recipients and probably also in patients with other autoimmune disorders, e.g., inflammatory bowel disease. No previous study has specifically investigated the risk of NMSC in MG patients treated with azathioprine. DESIGN/METHODS: Case-control study based on Danish population-based registries. Cases were MG patients with a first time diagnosis of NMSC during 2004-2009. Age- and sex-matched controls were selected among MG patients with no history of cancer using incidence density sampling. Prior use of azathioprine in cases and controls was assessed through prescription records (1995-2009). We used conditional logistic regression to calculate odds ratios (OR) with 95% confidence intervals (CI) for skin cancer associated with a high cumulative dose (≥150 g) or long-term use (≥5 years) of azathioprine, adjusted for confounders. RESULTS: We identified 30 cases and 360 matched controls. The prevalence of ever use of azathioprine varied between cases (53%) and controls (30%). Both high-cumulative dose (OR: 4.8; 95% CI: 1.7-13.6) and long-term (OR: 4.6; 95% CI: 1.7-12.6) use of azathioprine were associated with increased risk of NMSC compared with never use of the drug. CONCLUSIONS: Long-term use of azathioprine in MG patients increases the risk of NMSC. Disclosure: Dr. Pedersen has nothing to disclose. Dr. Pottegaard has nothing to disclose. Dr. Hallas has received personal compensation for activities with the Association of Danish Pharmaceutical Industry. Dr. Friis has nothing to disclose. Dr. Hansen has received royalty payments from ThermoFisher Scientific. Dr. Jensen has nothing to disclose. Dr. Gaist has nothing to disclose.