Metastatic metanephric adenoma with foci of papillary carcinoma in a child - A combined histologic, immunohistochemical, and FISH study

We report an example of metastatic metanephric adenoma containing foci of papillary carcinoma in the primitive tumor arising in the left kidney of an 11-year-old girl. Histology revealed a monomorphous population of small cells with bland cytology arranged in pseudoglandular, tubular, papillary, and glomeruloid structures with frequent psammoma bodies. Intermixed there were foci of and small cavities lined by larger cells with eosinophilic cytoplasm and larger nuclei with small nucleoli. A regional lymph node contained metastatic deposits with the former histologic pattern. By immunohistochemistry the small cells were negative for carcinoembryonic antigen (CEA) and keratin 7 while these antibodies reacted positively in the larger cells. A fluorescent in-situ hybridization (FISH) study for chromosome 17 in imprints from the primitive tumor revealed 3 signals in about 10% of the nuclei while the rest was disomic. Disaggregated cells from the metastatic lymph node consistently revealed 2 signals for chromosomes 7, 16, and 17. Histology of the primitive tumor resembled the epithelial component of the so-called metanephric adenofibroma while the metastatic lymph node exhibited histologic and FISH genomic features of metanephic adenoma.