Unusual leukemic presentation of rhabdomyosarcoma: report of two cases with immunological, ultrastructural and cytogenetical studies.

BACKGROUND: Bone marrow infiltration occurs rarely at presentation of rhabdomyosarcoma (RMS) or other childhood solid tumors. This possibility leads to misdiagnosis of leukemia and incorrect therapies might be administered. METHODS: We report two patients presenting with diffuse bone marrows involvement by neoplastic cells. Initial studies were not consistent with a diagnosis of leukemia and the cases were further studied extensively by indirect immunofluorescence, immunocytochemistry, electron microscopy and cytogenetics. RESULTS: In both cases blast cells were large, poorly differentiated, with immunological reactivity to the anti-desmin antibody. Ultrastructural findings of muscular features and chromosomal translocation t(2;13) (q37;q14) further confirmed the diagnosis of rhabdomyosarcoma of the alveolar subtype. This was then confirmed histologically in one patient. CONCLUSION: This study stresses the utility of analyzing cases of morphologically undifferentiated marrow blast cells by various techniques, as well as investigating for different types of both hematological and solid neoplasms.