A leukemic presentation of alveolar rhabdomyosarcoma in a 52-year-old woman without an identifiable primary tumor.

A 52-year-old woman presented with fatigue and thrombocytopenia. Imaging studies were unremarkable with the exception of a positron emission tomography scan, which demonstrated intense F-18 fluorodeoxyglucose uptake fusing to the marrow. A bone marrow aspirate was notable for large discohesive cells with basophilic cytoplasm, and flow cytometric analysis identified a population of phenotypically unusual cells that coexpressed CD56 and CD71. Immunohistochemical findings in the marrow biopsy demonstrated that the neoplasm was alveolar rhabdomyosarcoma, further supported by the presence of a t(2;13). This unusual case demonstrates that leukemic presentations of rhabdomyosarcoma can occur in older adults in the absence of an identifiable primary tumor.