Desmoplastic Small Round Cell Tumor of the Sigmoid Colon

ABSTRACT

Desmoplastic small round cell tumor (DSRCT) is a distinctive disease with a multidirectional differentiation and an aggressive clinical course. It mostly occurs in mesothelial-lined sites, and tumors originating in the paratesticular region, pleura and central nervous system are rarely reported. We report a case of DSRCT occurring in the sigmoid colon of a 39-year-old man, which was difficult to distinguish from small cell neuroendocrine carcinoma. The tumor was characterized by small round cells with irregular nests, cords, or rosette-like structures in the striking desmoplastic stroma. Some tumor cells had a rhabdoid feature with eosinophilic cytoplasmic globules. The tumor cells showed immunoreactivity for cytokeratin, epithelial membrane antigen, vimentin, desmin, neuron-specific enolase and Leu-7. Electron microscopic finding revealed perinuclear globoid whorls of intermediate filaments pushing the nucleus eccentrically.