Spindle-Cell Proliferations of the Urinary Tract

In order to define the immunohistochemical features of spindle cell proliferations of the urinary tract, we studied 18 lesions of this type with a panel of antibodies to epithelial and mesenchymal determinants. Histologically, 13 cases showed features that were not conclusively those of either spindle cell carcinoma or sarcoma, three contained overtly epithelial areas, and two were classified as "postoperative spindle cell nodules" (PSCN). Nine tumors in the indeterminate group and three with focally overt carcinomatous growth stained for cytokeratin and epithelial membrane antigen (EMA) and were classified as carcinomas. Eleven of these coexpressed vimentin, but desmin and muscle-specific actin were undetectable. The four remaining indeterminate neoplasms expressed desmin and muscle-specific actin as well as vimentin, but they lacked epithelial markers; these were categorized as leiomyosarcomas. Both PSCN were reactive for cytokeratin with each of three separate monoclonal antibody preparations. Desmin, actin, and vimentin were also observed in such lesions, but EMA was not. Because spindle cell proliferations may be difficult to interpret in routinely stained tissue sections, the additional information provided by immunohistochemical studies is helpful in establishing a diagnosis and separating biologically disparate lesions.