Metastatic metanephric adenoma in a child.

Metanephric adenoma is a recently characterized renal tumor that generally occurs in adults and has an excellent prognosis. To date, only one atypical metanephric adenoma has been reported to metastasize. The authors report a case of typical metanephric adenoma that arose in the left kidney of a 7-year-old girl that was associated with metastases to the para-aortic, hilar, and aortic bifurcation lymph nodes. The tumor was 9.5 cm and was composed entirely of epithelial elements arranged in tubules, short papillae, and glomeruloid bodies with scattered psammoma bodies. No atypia and only rare mitotic activity were present. Immunohistochemically, the tumor was negative for epithelial membrane antigen, negative for keratin AE1, and focally positive for both keratin CAM5.2 and cytokeratin 7. Tumor cytogenetics revealed a normal diploid karyotype, and disomy of chromosomes 7 and 17 was confirmed by fluorescence in situ hybridization. The authors conclude that tumors with histologic, immunohistochemical, and genetic features characteristic of typical metanephric adenoma can present with metastatic disease.