Undifferentiated rhabdomyosarcoma with lymphoid phenotype expression.

Poorly differentiated rhabdomyosarcomas are traditionally distinguished from lymphomas by their absence of lymphoid markers such as immunoglobulin or CD20 expression. We have encountered three alveolar rhabdomyosarcomas that were initially diagnosed as lymphoid neoplasms because of the expression of a lymphocytic phenotype in morphologically undifferentiated tumor cells. Subsequent cytogenetic analysis revealed a t(2; 13) in two cases. All cases recurred in the chest wall and showed positivity for muscle markers, such as muscle-specific actin, myoglobin, MyoD1, and/or desmin on subsequent immunohistochemistry. The findings in these three cases lead us to conclude that the presence of a lymphoid phenotype does not absolutely exclude the diagnosis of rhabdomyosarcoma.