Extrathymic tumors in patients with myasthenia gravis: a 35-year retrospective study

Autoimmune diseases are frequently associated with malignant tumor. In addition, prolonged immunosuppression may favor the development of malignancy. While the coincidence of myasthenia gravis and extrathymic tumor has been reported, the risk and features of these tumors are not well understood.

We treated 305 patients with myasthenia gravis from 1968-2003, including 48 thymoma cases. Two hundred twenty-nine patients had undergone thymectomy and 76 had not. We examined cancer risk, tumor characteristics, and associations to medications. We encountered 9 cases of extrathymic tumor. Cancer risk in the thymoma cases was 6.3% and 2.3% in the nonthymoma cases, a statistically insignificant difference. Azathioprine was administered to only 14 in this series of patients; however, 2 patients developed cancer.

Cancer risk in patients with myasthenia gravis is 2.6%, similar to that of the general population in Japan. We neurologists need to be aware that prolonged immunosuppression may favor the development of malignancy.