Metanephric adenoma of the kidney: an electron microscopic and immunohistochemical study with quantitative DNA...

Metanephric adenoma of the kidney is a newly recognized entity of renal adenoma, and the electron microscopic and immunohistochemical features of the tumor have not yet been well elucidated. The authors experienced a typical case of renal metanephric adenoma and studied the electron microscopic and immunohistochemical features of the tumor together with the DNA content of the tumor cells. Electron microscopically, the tumor was composed of immature epithelial cells with relatively uniform size, poor nuclear polarity, and scant cytoplasmic organelles arranged in small tubular or rosette pattern. Immunohistochemically, the cytoplasm of the majority of the tumor cells was positive for S-100, and occasionally for alpha-1-antitrypsin and vimentin. The tumor cells were also positive for cytokeratin, lysozyme, and Leu 7, with predominantly 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 immunohistochemical characteristics are quite similar to those of S-shaped body of the fetal kidney. An analysis of the nuclear DNA of the tumor cells by image cytometry revealed that the tumor entirely consisted of diploid cells' and lacked aneuploid cells. These results indicate that renal metanephric adenoma is composed of immature renal epithelial cells.