A Case of Cd20 Positive Mediastinal Rhabdomyosarcoma

We present the case of a 16-year-old boy admitted with a large mediastinal mass.Both in the mediastinal tru-cut biopsy and the bone marrow biopsy, a malignantsmall round cell tumor was determined. The clinical diagnosis was leukemia orlymphoma. The cytoplasmic CD20 expression was shown on the tumor cells of themediastinal tru-cut biopsy. Rhabdomyosarcoma was diagnosed by the flowcytometric analysis and immunohistochemical demonstration of muscle markers.Rhabdomyosarcomas are traditionally distinguished from lymphomas by theirabsence of lymphoid markers such as CD20. But in this case we have encounteredCD20 expression in the tumor cells. This finding lead us to conclude that thepresence of a lymphoid phenotype does not absolutely exclude the diagnosis ofrhabdomyosarcoma.