[Thymic cyst with elevated SLX levels in serum and cystic fluid]

A 24-year-old man was admitted to our hospital in June 1996 with complaints of anterior chest discomfort. Chest X-ray films on admission showed an abnormal mediastinal shadow with well-defined margin. Chest X-ray examinations about 6 weeks earlier had not detected any abnormalities. Laboratory tests on admission showed a high serum concentration of Siaryl Lewis X-i antigen (SLX). A computed tomographic scan of the chest showed a large (6 x 6 x 12 cm) homogeneous mass in the right anterior mediastinum. The mass was removed completely and histologically diagnosed as a thymic cyst. Biochemical analysis of fluid from the cyst revealed remarkably high levels of SLX, CA 19-9, and CEA. In immunohistochemical studies, epithelial cells from the cystic walls stained positive for SLX, CA 19-9, and CEA. After the operation, the level of serum SLX returned almost to normal.