Use of azathioprine for non-thymoma myasthenia and risk of cancer: a nationwide case-control study in Denmark

Eur J Neurol. 2013 Jun;20(6):942-8. doi: 10.1111/ene.12108. Epub 2013 Feb 28.


Background and purpose: To evaluate the association between the use of azathioprine and risk of cancer in patients with non-thymoma myasthenia gravis (MG) in a nationwide setting.

Methods: Case-control study based on population-based registries. Cases were patients with MG with a first time diagnosis of cancer (except non-melanoma skin cancer) registered during 2000-2009, and controls were patients with MG with no history of cancer. Prior use of azathioprine in cases and controls was assessed through prescription records (1995-2009). We used unconditional logistic regression to calculate odds ratios (ORs) with 95% confidence intervals (CIs) for cancer associated with a high cumulative dose [≥ 1000 defined daily doses (DDD)] or long-term use (≥ 5 years) of azathioprine, compared with never use of the drug and adjusted for potential confounders.

Results: We identified 89 cases and 873 controls. The prevalence of ever use of azathioprine was similar among cases (39.3%) and controls (39.4%). We observed a slightly elevated OR for cancer overall associated with long-term use of azathioprine (1.22; 95% CI: 0.62-2.40, P = 0.56). The highest ORs were observed for use of 2000 DDD or more of azathioprine; however, these risk estimates were based on small numbers.

Conclusions: Use of azathioprine in patients with non-thymoma MG may be associated with a slightly increased risk of cancer overall. Larger studies are necessary to address the risk of site-specific cancers.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Azathioprine / adverse effects*
  • Case-Control Studies
  • Denmark / epidemiology
  • Female
  • Humans
  • Male
  • Middle Aged
  • Myasthenia Gravis / drug therapy*
  • Myasthenia Gravis / epidemiology*
  • Neoplasms / chemically induced*
  • Neoplasms / epidemiology*
  • Registries
  • Risk Factors
  • Thymoma
  • Thymus Neoplasms


  • Azathioprine