[Alveolar rhabdomyosarcoma presenting as acute leukemia]

Rhabdomyosarcoma is the most common soft tissue sarcoma in adolescence and childhood, which manifests by the locally destructive growth of the primary tumor or its metastases. We report on a 29-year-old man with an alveolar rhabdomyosarcoma presenting with an unusual leukemia-like picture. On admission, the patient suffered from diffuse bone pain and renal insufficiency. Peripheral blood analysis showed anaemia, thrombocythaemia and blast-like cells. A bone marrow aspirate revealed extensive infiltration by atypical blast-like cells which were interpreted as acute lymphoblastic leukemia. Although confirmation of this diagnosis by immunophenotyping did not succeed chemotherapy was started immediately and led to partial remission. Histologic analysis of a bone marrow biopsy from the iliac crest, however, revealed an extensive solid tumor with alveolar spaces, lined by primitive round cells with positive PAS-reaction in the cytoplasm. Immunostaining demonstrated a positive reaction of the tumor cells for desmin and in a few tumor cells for smooth-muscle-actin. Chromosomal analysis showed a t(2;13) translocation typical for alveolar rhabdomyosarcoma. Although multiple lytic lesions of the skeletal system became evident during the further clinical course, the site of origin of the primary tumor could not be defined retrospectively. In conclusion, rhabdomyosarcoma should be included in the differential diagnosis of systemic diseases with extensive bone marrow infiltration by tumor cells that could otherwise be misinterpreted as a haematologic malignancy.