Myasthenia and Risk of Cancer: A Population-Based Case-Control Study (P7.010)

Objective: To evaluate the association between having non-thymoma myasthenia and the risk of extra-thymic cancer in a population-based setting. Backgroud: Approximately 10% of myasthenia patients harbour a thymoma, and these patients are at increased risk of extra-thymic cancer. However, whether non-thymoma myasthenia per se is linked to an increased risk of extra-thymic cancer is also of interest. Methods: We conducted a nationwide case-control study in Denmark based on medical registries. The study included all cases with a first time diagnosis of cancer during 2000-2009. Each case was matched by birth year and gender with eight population controls using risk set sampling. Through a validated register-based algorithm we identified subjects with myasthenia. We used conditional logistic regression to compute crude and adjusted odds ratios (OR), with 95% confidence intervals (CI), for cancer associated with a prior diagnosis of myasthenia. Results: We identified 233,369 cases and 1,866,634 controls. A total of 80 cases and 518 controls had a prior diagnosis of myasthenia. Myasthenia was not associated with an increased risk of overall cancer (OR: 1.1; 95% CI: 0.9-1.4). Adjusted ORs for major cancer sites were also close to unity, whereas we observed an elevated risk of lymphomas (OR, 2.0; 0.8-5.5). Early-onset myasthenia was associated with a slightly increased OR for overall cancer (1.5; 95% CI: 1.0-2.3), however, this estimate was based on small numbers. Conclusion: Non-thymoma myasthenia was not associated with an increased risk of overall cancer. Larger studies are necessary to evaluate the association between myasthenia and risk of lymphoma and potential effect modification by age of myasthenia onset in relation to cancer risk. 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.