The malignant potential of the dysgenetic germ cell in Klinefelter's syndrome.

We report two cases of extragonadal germ cell tumors in patients with Klinefelter's syndrome and review the other cases of germ cell tumors reported in this syndrome. Especially in choriocarcinoma, the presence of Klinefelter's syndrome may be overlooked because of the similar clinical presentations and testicular histology. We recommend karyotypes be carried out in patients with germ cell tumors since the dysgenetic gonad of Klinefelter's syndrome may be important in the pathogenesis of these malignancies. Also patients with Klinefelter's syndrome should be followed closely because of their increased risk of development of germ cell tumors.