Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children younger than 15 years. According to the World Health Organization, there are embryonal, alveolar and pleomorphic types of RMS. Most RMS patients present with a tumor mass in the head and neck region, urogenital tract or lower extremities. Unusual clinical presentation of the disease with massive bone marrow infiltration at the disease onset and mimicking hematologic neoplasm is rarely seen. A case is presented of a

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... -old, previously healthy girl hospitalized for outpatiently detected leukocyte elevation. For the last two weeks, she had complained of fatigue, myalgia and frequent bruising. On admission, clinical examination revealed numerous petechiae and hematomas, enlarged left inguinal lymph node and palpable spleen 2 cm below left costal arch. Laboratory findings showed leukocytosis, anemia and thrombocytopenia. Bone marrow fine needle aspiration (FNA) produced a hypercellular bone marrow sample with suppression of all three hemocytopoiesis lines and bone marrow infiltration with numerous undifferentiated tumor cells. Considering the morphological, cytochemical and phenotypic characteristics, the cytologic diagnosis was: bone marrow infiltration with RMS cells. Abdominal computerized tomography revealed a primary tumor occupying the entire retropeoritoneal space. Tumor biopsy confirmed alveolar subtype of RMS. In conclusion, in cases of bone marrow infiltration with primitive, immature cells, RMS should be considered as differential diagnostic possibility. Adjuvant technologies (cytochemistry, immunocytochemistry, cytogenetic analysis, flow cytometry, and molecular analysis) can be very helpful in diagnostic work-up, and may lead to definitive diagnosis in some cases.