The expanding clinical spectrum of desmoplastic small round-cell tumor: a report of two cases with molecular confirmation.

Desmoplastic small round cell tumor (DSRCT) is an aggressive neoplasm characterized by a consistent histological appearance, a unique immunohistochemical profile, and a specific chromosomal translocation. DSRCT is also hallmarked by distinctive clinical features. Most tumors arise in adolescent or young adult males, present as bulky abdominal masses, and diffusely spread along the peritoneal surface. We report two cases of DSRCT that do not fit this typical profile. One case involved the abdominal cavity of a 76-year-old woman. The other case arose in the parotid of a 22-year-old man. Histologically, the tumors showed the characteristic features of DSRCT. Immunohistochemically, the tumors showed positivity for cytokeratin, desmin, and neuron-specific enolase. Genetically, the tumors expressed the EWS-WT1 chimeric transcript. These two cases expand the differential diagnosis for poorly differentiated small-cell tumors that involve elderly patients or arise in the parotid. Moreover, they challenge the popular notion that DSRCT is a "blastomatous" tumor derived exclusively from the primitive mesothelium.