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Differential Diagnosis: The main differential diagnosis of metanephric adenoma (MA) is epithelial-predominant Wilms tumor (WT) in pediatric patients and solid variant of papillary renal cell carcinoma (sPRCC) in adults. An immunohistochemical panel consisting of WT1, CD57, CK7, and AMACR, in conjunction with H&E-stained slides, can resolve most of the cases.
sPRCC: It is often multifocal and has fibrous pseudocapsule. The nuclear grade is higher than that seen in MA. Prominent nucleoli are frequent. The cells have moderate amount of pink cytoplasm which gives the tumor a more eosinophilic appearance (in contrast to the scant cytoplasm in MA which makes it appear quite basophilic). Immunohistochemical profile of sPRCC is: WT1-ve, CD57-ve, CK7+, and AMACR+ve. MA has the opposite pattern (WT1+, CD57+, CK7-ve, and AMACR-ve). sPRCC also shows gain of chromosome 7 and 17 and loss of Y by FISH. These chromosomal changes are absent in MA.
sPRCC: It is often multifocal and has fibrous pseudocapsule. The nuclear grade is higher than that seen in MA. Prominent nucleoli are frequent. The cells have moderate amount of pink cytoplasm which gives the tumor a more eosinophilic appearance (in contrast to the scant cytoplasm in MA which makes it appear quite basophilic). Immunohistochemical profile of sPRCC is: WT1-ve, CD57-ve, CK7+, and AMACR+ve. MA has the opposite pattern (WT1+, CD57+, CK7-ve, and AMACR-ve). sPRCC also shows gain of chromosome 7 and 17 and loss of Y by FISH. These chromosomal changes are absent in MA.