Mediastinal immature teratoma with yolk sac tumor and myelomonocytic leukemia associated with Klinefelter's syndrome.

A 14-year-old male presenting with a short history of right subclavicular chest pain was found to have a mediastinal tumor. Hematologic investigations and bone marrow examination showed features of myelomonocytic leukemia. The mediastinal tumor was excised, but the surgery was complicated by massive hemorrhage. The patient's condition deteriorated postoperatively and he died a week later. The histology of the mediastinal tumor showed the typical features of an immature teratoma with a yolk sac tumor. A prominent infiltrate of leukemic blast cells was present within blood vessels and in close proximity to the yolk sac component. The karyotypic analysis of leukemic cells isolated and cultured from the bone marrow showed 50XXY, +8, +21, +iso G-group marker chromosome karyotype.