Primary undifferentiated carcinoma of the small intestine: an immunohistochemical study and review of the literature.

Primary undifferentiated carcinoma of the small intestine is an extremely rare neoplasm. Here, we report a case of primary undifferentiated carcinoma that arose from the ileum in a 65-year-old woman. Laboratory data revealed anemia and slightly elevated inflammatory parameters. Computed tomography showed a heterogeneous mass in the pelvic cavity, and magnetic resonance imaging revealed that the margin of the tumor mass was clear. Positron emission tomography using (18)F-fluoro-2-deoxy-D: -glucose (FDG) showed accumulation of FDG on the tumor mass with a standardized uptake value of 8.3. Partial resection of the ileum to remove the tumor was performed under a clinical diagnosis of small intestinal carcinoma. The tumor was nodulated and had a circumscribed margin 6.5 x 5.5 x 4 cm in diameter. Microscopically, the tumor was composed of giant polygonal cells with cellular atypia. Immunohistochemical examination revealed that the tumor cells expressed epithelial markers including AE1/AE3, CAM5.2, and EMA; however, lymphocytic, mesenchymal, and gastrointestinal stromal tumor markers were not expressed. We made a final diagnosis of primary undifferentiated carcinoma of the small intestine. The prognosis of patients with undifferentiated carcinoma of the small intestine is very poor. To improve the outcome of treatment, early and accurate diagnosis is essential, and additional therapy, including multimodality adjuvant therapy or the administration of novel molecular targeted drugs, should be considered.