We report a case of extramedullary plasmacytoma of the maxilla, which was difficult to diagnose definitively by conventional histopathology because of the presence of epithelial antigens. A 62-year-old male with a 7-month-history of unilateral epiphora and nasal obstruction followed by swelling of his left cheek is presented. Physical findings, CT scanning and MRI imaging revealed a maxillary tumor, T4N0M0. Blood test, serum and urine protein analyses and bone marrow examination showed no abnormality. No other systemic lesion was found in X-rays and 67Ga- and 99mTc-scintigrams. Exploratory resection was performed, and the tumor was pathologically diagnosed as an undifferentiated carcinoma on the basis of its morphological features and positive immunohistochemical examination for epithelial markers such as cytokeratin and epithelial membrane antigen (EMA). The patient received preoperative local irradiation of 40 Gy, and underwent total maxillectomy followed by irradiation of 50 Gy and administration of cisplatin and 5-fluorouracil. Nineteen months after the surgery, the patient manifested a tumor in the thyroid region with high serum gamma-globulin and IgG levels. In addition, IgG-kappa-type myeloma protein was detected by immunoelectrophoresis of the serum. The patient underwent subtotal thyroidectomy. Although the tumor cells of the surgical specimen still exhibited epithelial markers, electron microscopic observation, immunohistochemical examination and Southern blot analysis demonstrated rough endoplasmic reticulum-rich cytoplasm, kappa (+) lambda (-) of Ig light chain and rearranged bands of Ig heavy chain, which are characteristic of plasmacytoma. The tumor was, consequently, diagnosed as extramedullary plasmacytoma. Serum gamma-globulin and IgG levels returned to the normal range 4 months after the second surgery. In conclusion, we emphasize that plasmacytoma may express epithelial antigens, and thus the importance of multiple supplementary methods to diagnose this neoplasm.
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