Mediastinal yolk sac tumor: ultrastructural and immunofluorescent studies.

Primary mediastinal yolk sac tumor is rare. In this report, a case of a 32-year-old male with a mediastinal yolk sac tumor was studied by light, electron, and immunofluorescent microscopy. A positive immunofluorescent reaction to alpha-fetoprotein (AFP) correlated with the PAS-positive hyaline globules and electron-dense deposits seen in intracellular and extracellular locations. Serum AFP is a useful tumor marker for monitoring the results of therapy. Review of the literature indicates that the prognosis for patients with yolk sac tumor is generally poor.