Sarcomatoid carcinoma of the stomach. A report of three cases with immunohistochemical and ultrastructural observations

The authors report three cases of sarcomatoid carcinoma arising in the stomach. This uncommon tumor is characterized by a mixture of malignant epithelial and spindle cell elements. All three tumors were large (average diameter, 5 cm) and infiltrated deep into the stomach wall. Two of the tumors had a polypoid configuration; the third was ulcerated and endophytic. Intestinal metaplasia was present adjacent to the tumor in all cases, with dysplasia in two. Immunohistochemical studies showed positivity for cytokeratin, carcinoembryonic antigen, and epithelial membrane antigen in the epithelial component of all tumors, and Leu-M1 was positive in the epithelial component of one. The spindle cell components contained vimentin, and in tumor 2, the spindle cell component was also positive for desmin. Two tumors showed focal positivity for cytokeratin in the spindle cells immediately adjacent to the epithelial component. Ultrastructurally, the spindle cell component of two tumors was composed of undifferentiated cells without specific epithelial or mesenchymal features. The third tumor contained occasional cells with features of myofibroblasts.