Biphasic intra-abdominal desmoplastic small cell tumor in a patient with proximal spinal muscular atrophy.

A case is reported of intra-abdominal desmoplastic small cell tumor (IDSCT) with biphasic histologic features in a patient with proximal spinal muscular atrophy. The tumor was composed of small epithelial cell nests with spindle cell sarcomatous areas. Both areas were surrounded by a desmoplastic stroma. Immunohistochemical studies revealed reactivity for low molecular weight cytokeratin, epithelial membrane antigen, vimentin, desmin and Leu-7 in both areas. Electron microscopic examination demonstrated paranuclear aggregates of intermediate filaments, zonula adherens and basement membrane-like material in the epithelial cells, while spindle cells in the tumor had fewer intracytoplasmic organelles. However, intermediate or transitional forms of both types of tumor cells were frequently observed. Although IDSCT are known to express multi-phenotypes immunohistochemically, attention should be paid to the broad spectrum of cell morphology in these tumors.