Desmoplastic small round cell tumor of the pleura.

Three cases of desmoplastic small round cell tumor (DSRCT) with multiphenotypic differentiation, primary in the pleura, are presented. This is a previously unrecognized site for this tumor type. Two patients were male and one female aged 29, 24, and 17 years. All presented with chest pain and were found to have pleural-based tumors associated with pleural effusion. Abdominal involvement was not present in any of the cases. Histologically, the tumor showed the characteristic features of intra-abdominal DSRCT, including angulated nests of small cells embedded in a vascular fibroblastic stroma, focal rhabdoid phenotype, and areas of central necrosis. The neoplastic cells showed evidence of epithelial, mesenchymal, and neural differentiation with characteristic dot-like positivity for vimentin and desmin topographically corresponding to perinuclear aggregates of intermediate filaments identified on electron microscopy in one case. Two patients died of disease 2 years and 15 months after presentation, respectively, and one patient is alive with disease 18 months after presentation. The histogenesis of DSRCT is unknown. Most previously reported cases involved the peritoneum or tunica vaginalis, suggesting a histogenetic relationship to the mesothelium. The occurrence of these tumors in the pleura lends further support to this theory.