Endodermal sinus tumor of the mediastinum. Cytologic diagnosis on a pleural effusion.

A primary mediastinal endodermal sinus tumor in a young man was diagnosed by cytologic examination of a pleural effusion. Subsequent evaluation revealed a greatly elevated serum alphafetoprotein (AFP); computed tomographic scan of the chest showed a large anterior mediastinal mass. Routine examination of the smears and cell block preparations revealed clusters of tumor cells with a few intracytoplasmic hyaline droplets. Immunohistochemical stains for AFP, alpha-1-antitrypsin and cytokeratin were positive in the tumor cells while stains for carcinoembryonic antigen and the beta subunit of human chorionic gonadotropin were negative. This supported the diagnosis of endodermal sinus tumor, a rare primary tumor within the mediastinum.