[Myeloid Sarcoma of the Testis].

A 68-year-old man with swelling of his left testis was referred to our hospital. There was no history of hematologic disease. The diameter of the testicular mass was 40 mm. We performed a left orchiectomy. Histopathologic examination revealed diffuse infiltration of immature neoplastic cells with a high nuclearcytoplasmic ratio. Immunohistochemical analysis revealed that cells were positive for myeloperoxidase, while T-cell and B-cell markers were negative. There was no evidence of leukemia cells in peripheral blood or in bone marrow. The tumor was diagnosed as a testicular isolated myeloid sarcoma. Eleven months after the orchiectomy, enlargement of the para-aortic lymph node occurred. There was no evidence of leukemia cells in the peripheral blood or bone marrow. The patient is undergoing chemotherapy for recurrence of myeloid sarcoma. Myeloid sarcoma is an extramedullary tumor composed of immature myeloid cells. Myeloid sarcoma primarily involving the testis is rare. However, it is important to consider it as a differential diagnosis because it has a poor prognosis.