Extragonadal germ cell tumors are often associated with Klinefelter syndrome.

Klinefelter syndrome is a well documented abnormality of sex differentiation, with an incidence of 1 in 600 newborn males. It is characterized by a 47,XXY or a mosaic karyotype and clinical findings of hypergonadotrophic hypogonadism, small testes, infertility, reduced body hair, gynecomastia, and tall stature. Other conditions like venous disease, autoimmune disorders, mild neurobehavioral deficit, diabetes mellitus, sexual precocity, and osteoporosis may also affect these patients. Different malignancies such as breast cancer, testicular tumors, leukemia, and lymphomas occur in 1%-2% of the cases. Klinefelter syndrome has been associated with other malignancies such as extragonadal germ cell tumors; however, some authors consider this association an unusual finding. We report the molecular cytogenetic studies performed in 4 young males with mediastinal germ cell tumors. In 2 cases, a 47,XXY karyotype was recognized in different tissues by fluorescent in situ hybridization, whereas the other 2 had a normal XY karyotype. We propose that in young patients with mediastinal teratoma, a cytogenetic analysis must always be performed.