Desmoplastic small round cell tumor of the lung.

An extra-abdominal desmoplastic small round cell tumor (DSRCT) of the lung with immunohistochemical, ultrastructural, and cytogenetic evidence of multidirectional differentiation is reported. We demonstrate that DSRCTs of the lung and pleura show morphologic, molecular, genetic, and ultrastructural features similar to DSRCTs arising in other sites. The tumor showed coexpression of cytokeratins (AE1/3, epithelial membrane antigen, CAM 5.2) and mesenchymal markers (vimentin, desmin, neuron-specific enolase), as well as WT1. Ultrastructurally, intracytoplasmic whorls of intermediate filaments, similar to previous descriptions of DSRCT in nonthoracic sites, were also demonstrated in this case. EWS-WT1 gene fusion characteristic of DSRCT with the t(11;22)(q13;q12) translocation was demonstrated in this tumor.