SARCOMATOID CARCINOMA OF THE SMALL-INTESTINE - HISTOLOGIC, IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL FEATURES OF 3 CASES AND ITS DIFFERENTIAL-DIAGNOSIS

Three cases of sarcomatoid carcinoma of the small intestine are presen ted. One of them was found accidentally in the duodenum of a patient w ith a well differentiated adenocarcinoma and a malignant lymphoma that were limited to the stomach. The other two cases arose from the ileum . All of the tumors were whitish, soft and ulcerated with focal hemorr hage and necrosis and showed expansive growth. Each tumor consisted of a mixture of polygonal and spindle shaped anaplastic neoplastic cells arranged in sheet, short fascicular or haphazard fashion, with no fin ding suggesting epithelial differentiation. Special stains demonstrate d intracellular mucin in only a small number of tumor cells in two cas es, but not in the other case. Immunohistochemically, the tumor cells of two cases at both primary and metastatic sites showed a positive im munoreaction for cytokeratin and epithelial membrane antigen. In the o ther case, only a few tumor cells at the metastatic site, but not at t he primary site, showed cytokeratin positivity. Various numbers of tum or cells positive for vimentin, alpha-1-antitrypsin (AAT), alpha-1-ant ichymotrypsin (ACT) and KP-1 were detected in each case. Ultrastructur ally, some populations of tumor cells possessed various amounts of ton ofilaments with a few intercellular connections between adjacent tumor cells. These cases should be classified as sarcomatoid carcinoma of t he small intestine, despite partial or complete loss of epithelial fea tures, and distinguished from the various sarcomas.