[Differentiated papillary kidney tumors. Differentiation between metanephric adenoma and papillary adenoma]

Metanephric adenoma of the kidney is a well described tumor entity. The differential diagnosis between papillary adenoma or papillary carcinoma type 1 and metanephric adenoma of the kidney can be challenging in single cases. We report two cases of metanephric adenomas and compare their immunophenotype with a papillary adenoma. The analysis of these metanephric adenomas and a review of the literature shows that CD-57 positivity and lack of EMA expression are helpful in distinguishing metanephric adenoma from papillary adenoma and papillary carcinoma. Glomeruloid structures, Psammoma bodies, necrosis or expression of cytokeratin 7 and vimentin are common features in metanephric adenoma and papillary adenoma or papillary carcinoma. The knowledge of the immunohistochemical constellation is important, because metanephric adenoma can be very large and often have some necrosis.