Mediastinal germ cell tumor with secondary nongerm cell malignancy, and extensive hematopoietic activity. Pathology, DNA-ploidy, and karyotyping.

We report on a malignant germ cell tumor located in the anterior mediastinum. After chemotherapy the tumor was classified as residual teratoma with sarcomatous components. There was extensive hematopoiesis in the tumor tissue. The tumor cells had a modal chromosome number of 76; the only structural abnormality was a deletion of the long arm of chromosome 9. An i(12p) chromosome was lacking in this tumor. Karyotyping of peripheral blood and bone marrow occasionally showed metaphases with numerical and structural abnormalities, probably related to chemotherapy. The patient died within two years after the initial diagnosis, of a poorly differentiated hematopoietic malignancy, probably of myelomonocytic origin, based on morphology and the fact that non-specific esterase activity was demonstrated in the tumor cells. The karyotype of this malignancy was highly abnormal, but unrelated to that of the mediastinal malignant GCT. In this case there is no proof that the secondary malignancy was derived from the primary mediastinal malignant GCT. In view of the multiple aneuploid stem lines in the primary tumor, this possibility cannot be dismissed either.