A case of multiple thymoma: the possibility of intra-thymic metastasis.

A case of multiple thymoma is reported. The patient was a 28-year-old woman who came to us with myasthenia gravis. There were two separate thymoma in the anterior mediastinum: one measured 70 x 30 x 30 mm, while the other was 1.5 mm in diameter and situated in the surrounding thymic tissue. A histological study revealed that both thymoma consisted of epithelial cells with abundant cytoplasm, round-to-oval nuclei and inconspicuous nucleoli. Morphometric analysis showed the nuclear size of the epithelial cells to be similar in both tumors. The likelihood of positive Leu7 and keratin immunohistochemical staining was also similar for the two tumors. The two thymoma had similar histological, morphometric and immunohistochemical characteristics. These findings suggest the possibility of intra-thymic metastasis rather than a multicentric thymoma development. Extended thymectomy should be performed for thymoma to prevent postoperative tumor recurrence.