Choriocarcinoma, thyrotoxicosis, and the Klinefelter syndrome.

A patient with the combined features of Klinefelter syndrome, thyrotoxicosis and a primary mediastinal choriocarcinoma is reported. Review of the literature reveals that extragonadal germ cell tumors appear to be significantly associated with the Klinefelter syndrome. The reason for this is presently unclear but may involve an unusual propensity of the extragonadal aneuploid germ cell to undergo malignant degeneration.