[A case of mediastinal growing teratoma syndrome with acute megakaryoblastic leukemia].

We report a case of a 38-year-old man who was diagnosed with a mediastinal germ cell tumor. After induction chemotherapy, the tumor marker levels normalized, but the tumor itself continued to grow. Surgical resection was performed successfully, but the patient developed acute megakaryoblastic leukemia 6 months later, and induction and consolidation therapies failed to achieve remission. Leukemia cells invaded the central nervous system following hematopoietic stem cell transplantation, and the patient died 5 months after being diagnosed with leukemia. This very rare case of a mediastinal germ cell tumor met the criteria for "growing teratoma syndrome", against a background of acute megakaryoblastic leukemia.