[Alveolar rhabdomyosarcoma of unknown origin mimicking acute leukemia at the initial presentation].

A 14-year-old boy presented with a short history of general fatigue. Laboratory examination of the peripheral blood revealed white blood cells 11,300/microl, hemoglobin 10.4 g/dl, platelets 45,000/microl, fibrinogen < 50 mg/dl, fibrin/fibrinogen degradation products 536 microg/ml and lactate dehydrogenase 1,684 U/l. A bone marrow aspirate contained 89.6% of undifferentiated tumor cells. A hematological malignancy was suspected and the patient was treated with idarubicin and cytarabine. However, further examination revealed that tumor cells were positive for CD56 and lacked lineage markers of lymphoid or myeloid cells. They were positive for PAS, HHF35 and desmin, and negative for MPO. Reverse transcriptase polymerase chain reaction demonstrated PAX3/FKHR fusion transcripts, confirming the diagnosis of alveolar rhabdomyosarcoma. Radiological examination revealed only one enlarged lymph node being 1.5 cm in diameter at the paraaortic region in the abdomen, and failed to find a primary tumor. After three courses of chemotherapy containing etoposide, cyclophosphamide, pirarubicin, cisplatin and vincristine, tumor cells were eradicated from the bone marrow. The patient received an allogeneic bone marrow transplantation eight months after diagnosis, although he died of hepatic veno-occlusive disease on day 21. Alveolar rhabdomyosarcoma often develops in older children and younger adults, and its bone marrow infiltration may mimic acute leukemia.