Desmoplastic small cell tumors of the peritoneum coexpressing mesenchymal and epithelial markers.

Desmoplastic small cell tumors arising diffusely within the abdomen and lacking an apparent organ of origin are rare. Most previously reported cases occurred in children, but young adult patients also have been described. Light microscopic examination shows the tumors to be composed of nests of small cells surrounded by an abundant desmoplastic stroma. Immunohistochemical findings reveal multidirectional differentiation with coexpression of cytokeratin, milk fat globule, neuron-specific enolase, Leu-7, desmin, and vimentin. Electron microscopic examination demonstrates paranuclear condensations of intermediate filaments. The authors describe two patients who died of their disease, despite aggressive chemotherapy and surgical intervention.