[An undifferentiated carcinoma of the stomach--a report of 2 cases].

Two cases of an undifferentiated carcinoma of the stomach have been investigated by conventional histologic, immunohistochemical, and ultrastructural methods. The patients were a 73-year-old man and 65-year-old man. A postoperative histological examination of the resected stomach of each patient disclosed large areas of an undifferentiated carcinoma which were relatively well demarcated from areas of the adenocarcinoma. In the undifferentiated carcinomatous areas, the reticulin fiber stain was epithelial in pattern, and mucin staining proved negative. Similarly both Grimelius and Fontana-Masson staining also negative. In like manner immunostains using cytokeratin , vimentin , IgG, IgA, s-100 protein, and NSE were all negative, and an electron microscopic study showed no neurosecretory granules or mucin secretory granules. Based on these findings, the diagnosis of either a malignant lymphoma or small cell anaplastic carcinoma could be excluded, and thus an undifferentiated carcinoma was the determination.