METANEPHRIC ADENOMA OF THE KIDNEY - AN ELECTRON-MICROSCOPIC AND IMMUNOHISTOCHEMICAL STUDY WITH QUANTITATIVE DNA MEASUREMENT BY IMAGE-ANALYSIS

Metanephric adenoma of the kidney is a newly recognized entity of rena l adenoma, and the electron microscopic and immunohistochemical featur es of the tumor have not yet been well elucidated. The authors experie nced a typical case of renal metanephric adenoma and studied the elect ron microscopic and immunohistochemical features of the tumor together with the DNA content of the tumor cells. Electron microscopically, th e tumor was composed of immature epithelial cells with relatively unif orm size, poor nuclear polarity, and scant cytoplasmic organelles arra nged in small tubular or rosette pattern. Immunohistochemically, the c ytoplasm of the majority of the tumor cells was positive for S-100, an d occasionally for alpha-1-antitrypsin and vimentin. The tumor cells w ere also positive for cytokeratin, lysozyme, and Leu 7, with predomina ntly cell membrane staining. Only tumor cells arranged in papillary or large tubular pattern were positive for epithelial membrane antigen ( EMA). Tumor cells were negative for Leu M1 and HMB-45. These immunohis tochemical characteristics are quite similar to those of S-shaped body of the fetal kidney. An analysis of the nuclear DNA of the tumor cell s by image cytometry revealed that the tumor entirely consisted of dip loid cells and lacked aneuploid cells. These results indicate that ren al metanephric adenoma is composed of immature renal epithelial cells.