[A case of thymic cyst showing elevated CEA, SLX and CA125 levels in the cystic fluid associated with non-invasive thymoma].

A 66-year-old woman, who had complained of left ptosis and been diagnosed as having myasthenia gravis (ocular type) 9 years previously, was admitted to our hospital for further examination of an abnormal mass shadow on chest X-ray film. Chest computerized tomography (CT) revealed a cystic tumor in the anterior mediastinum and thoracotomy was performed to make a definitive diagnosis. The tumor could be removed completely and was diagnosed histologically as a thymic cyst with thymoma. The cyst was 32 x 30 x 28 mm in size and contained about 10 ml of brown turbid fluid. The levels of CEA (61.3 ng/ml), SLX (24,000 U/ml) and CA125 (1300 U/ml) were markedly increased in the cystic fluid, while those in serum were not elevated. Immunohistochemical staining demonstrated the epithelial cells lining the cyst to contain SLX. The findings suggest that SLX was produced in the epithelial cells of the cyst. However, neither CEA nor CA125 was positive in the epithelial cells. From our review of reported cases of thymic cyst showing elevated levels of tumor markers in the cystic fluid, the main mechanism of marked elevation of tumor markers seems to be condensation in the cystic fluid rather than increased production in epithelial cells lining the cyst. Cases of thymic cyst with thymoma are extremely rare, but our case was concluded to be incidentally associated with non-invasive thymoma.