Abstract
Computed tomography examination of a 17-year-old male who complained of frequent episodes of fever and chest pain revealed an anterior mediastinal tumor. This tumor was diagnosed to be a non-seminomatous germ cell tumor based on the elevated level of AFP in the serum and by percutaneous needle biopsy. After two courses of chemotherapy with CDDP and VP-16, the serum AFP level reduced to almost the normal limit. However, the tumor size was found to have increased on a CT scan, and the patient complained of dyspnea. We completely resected the tumor via a median sternotomy. Pathological findings revealed a mature teratoma with massive necrosis, a certain amount of embryonal carcinoma, and immature mesenchymal tissue. Four months after the operation, the patient complained of arthalgia of the limbs and low-grade fever. Close examination revealed no sign of tumor recurrence or metastasis, and the AFP level was normal. However, the number of platelets in the peripheral blood had decreased, and the serum LDH level was apparently increased. A bone marrow biopsy revealed megakaryocyte-like atypical cells. These cells were CD31- and CD41-positive; therefore, acute megakaryoblastic leukemia (M7) was diagnosed. The features of the atypical cells were similar to those of the immature mesenchymal cells in the germ cell tumor, which were also CD31- and CD41-positive. From these results, it is supposed that the atypical cells in the bone marrow were clones of the mesenchymal cells in the germ cell tumor. In other words, the etiology of M7 was considered to be bone marrow metastasis.
