Metaplastic thymoma with myasthenia gravis presumably caused by an accumulation of intratumoral immature T cells: a case report.

Among human neoplasms, thymomas are well known for their association with paraneoplastic autoimmune diseases such as myasthenia gravis. However, regarding rare metaplastic thymoma, only one case of an association with myasthenia gravis has been reported. Here, we present the second case of a 44-year-old woman with metaplastic thymoma associated with myasthenia gravis. In metaplastic thymoma, intratumoral terminal deoxynucleotidyl transferase-positive T-cells (immature T-cells) are generally scarce, while they were abundant in the present case. We believe that these immature T-cells could be related to the occurrence of myasthenia gravis.