Cytologic and fluorescence in situ hybridization (FISH) examination of metanephric adenoma.

Metanephric adenoma is a recently described benign renal neoplasm with distinctive histologic features. The cytologic appearance and fluorescence in situ hybridization (FISH) studies of this tumor have not been described. We present a case from a 48-yr-old woman. Cytologically, the cells were arranged in tight, short papillae and loose sheets. The cells had scant cytoplasma, round monotonous nuclei with fine even chromatin and rare small nucleoli. Immunohistochemistry revealed no reactivity for epithelial membrane antigen (EMA), keratins (AE1/AE3, callus, 34BE12), or carcinoembryonic antigen (CEA). FISH showed a disomic pattern for chromosomes 7, 17, and for the chromosome 3 short arm. The differential diagnosis includes Wilms' tumor, renal adenoma, papillary renal cell carcinoma, and metastatic tumors. Both immunohistochemistry and FISH may be of help in distinguishing some of these lesions.