Rhabdomyosarcoma mimicking acute leukemia in an adult: report of a case with histologic, flow cytometric, cytogenetic, immunohistochemical, and ultrastructural studies.

A case of a 25-year-old man who presented with low back, knee, and hip pain with bruising, leukocytosis, and thrombocytopenia is reported. Histopathologic and flow cytometric studies revealed a malignant neoplasm, which was thought to be consistent with an unusual type of acute leukemia. Subsequent immunohistochemical studies revealed diffuse bone marrow involvement by rhabdomyosarcoma, demonstrated by positivity for desmin and muscle-specific actin. In addition, the diagnosis of metastatic rhabdomyosarcoma was confirmed with cytogenetic and ultrastructural studies. The incidence of rhabdomyosarcoma, a disease usually seen in childhood, presenting with extensive bone marrow involvement and mimicking acute leukemia in an adult is extremely rare. This case highlights the need to consider rhabdomyosarcoma in the differential diagnosis in patients who present with a leukemic picture and atypical blasts that lack the usual hematopoietic markers.