Gastrointestinal stromal tumor of the stomach with rhabdoid phenotype: immunohistochemical, ultrastructural, and immunoelectron microscopic evaluation.

A variety of neoplasms with rhabdoid differentiation have been reported in many sites. The authors describe a case of gastrointestinal stromal tumor (GIST) of the stomach that exhibited prominent rhabdoid features. Immunohistochemically, the tumor cells displayed positive staining for vimentin, c-kit, CD34, and alpha smooth muscle actin. Ultrastructural examination of the rhabdoid tumor cells revealed paranuclear whorls of intermediate filaments, which were immunoreactive for vimentin by both light microscopic immunohistochemical and protein A gold immunoelectron microscopic techniques. On H&E light microscopic examination alone, such a tumor could be mistaken for a variety of epithelial, mesenchymal, or other neoplasms that may show rhabdoid features. One report of GIST with a rhabdoid histologic phenotype has been described. This is the second known report of such a case with immunophenotypic and ultrastructural evaluation, and the first case with immunoelectron microscopic examination.