A case of thymic cyst with elevated sialylated Lewis X-i, carbohydrate antigen 19-9 and tissue polypeptide antigen in the cystic fluid with no elevation of serum tumor markers.

A 56-year-old man, tentatively diagnosed as having cardiomegaly, was found to have a large cyst in the left anterior mediastinum. At thoracotomy a multilocular cystic mass containing a colorless serous fluid was found and resected. Histologically, the cyst was lined with flattened epithelial cells, and thymic tissue was present in the cyst's wall; a diagnosis of thymic cyst was made. There were no malignant components or inflammatory changes. Sialylated Lewis X-i (SLX), carbohydrate antigen 19-9 (CA19-9) and tissue polypeptide antigen (TPA) in the cystic fluid were markedly elevated, while the serum concentrations of these tumor markers were within the normal ranges. Immunohistochemical studies showed the epithelial cells lining the cyst to contain CA19-9 and SLX. The findings suggest the tumor markers to have originated in the thymic epithelium lining the cyst.