Metanephric adenoma, nephrogenic rests, and Wilms' tumor - A histologic and immunophenotypic comparison

Metanephric adenoma (MA) is a renal tumor that is generally detected in adu lts and occasionally in children. These tumors usually behave in a benign f ashion. Although the histogenesis of MA is unclear, a morphologic similarit y to Wilms' tumor (WT) complex exists. Six cases of MA, five cases of child hood WT (CWT), two cases of adult WT (AWT), and four cases of treated MWT a nd/or nephrogenic rests (MWT/NR), with paraffin blocks available for use, w ere retrieved from the surgical pathology files of the Mayo Clinic. Clinica l information was extracted from the medical record. Immunoperoxidase stain s for WT1, AE1, CK7, CD57, CD56, and desmin were performed on paraffin sect ions from all cases. All six cases of MA were strongly and diffusely positi ve with antibodies to WT1 and CD57 and focally positive with antibodies to CK7. Three cases showed focal faint staining in <5% of the cells with kerat in AE1. Stains for CD56 and desmin were negative. All seven cases of WT, in cluding five CWT and two AWT, were strongly and diffusely positive with WT1 in the blastema and epithelium but showed only weak focal positivity in st romal cells. Six cases were diffusely positive for CD56 and one case showed focal positivity. Keratin AE1 was positive in one case of AWT and focally positive in the other AWT. The blastema of all cases of WT were negative fo r desmin, CK7, and CD57, although staining for keratin AE1, CD56, and CD57 was seen in maturing tubules of CWT cases. Of the five CWT cases, two had a ssociated NR and two showed maturing WT after treatment. The areas of NR an d maturing WT were histologically similar to MA and were composed of small tubules with uniform nuclei with no mitotic activity, scant cytoplasm, and focal calcifications. All four cases of maturing WT/NR were positive for WT 1 and focally positive for CD57, CK7, and AE1 Stains for CD56 and desmin we re negative except in foci of residual blastema, which stained for CD56 but lacked CD57 and CK7 staining. Five cases each of renal cell carcinoma, pap illary renal cell carcinoma, and oncocytoma were negative for WT1. Two of f ive cases of chromophobe carcinoma showed very weak staining present in < 1 0% of tumor nuclei. Metanephric adenoma is histogenetically related to WT a nd is morphologically and immunophenotypically identical to maturing WT and nephrogenic rests.