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 p apillary carcinoma in the primitive tumor arising in the left kidney of an 11-year-old girl. Histology revealed a monomorphous population of small cel ls with bland cytology arranged in pseudoglandular, tubular, papillary, and glomeruloid structures with frequent psammoma bodies. Intermixed there wer e foci of and small cavities lined by larger cells with eosinophilic cytopl asm and larger nuclei with small nucleoli. A regional lymph node contained metastatic deposits with the former histologic pattern. By immunohistochemi stry the small cells were negative for carcinoembryonic antigen (CEA) and k eratin 7 while these antibodies reacted positively in the larger cells. A f luorescent in-situ hybridization (FISH) study for chromosome 17 in imprints from the primitive tumor revealed 3 signals in about 10% of the nuclei whi le the rest was disomic. Disaggregated cells from the metastatic lymph node consistently revealed 2 signals for chromosomes 7, 16, and 17. Histology o f the primitive tumor resembled the epithelial component of the so-called m etanephric adenofibroma while the metastatic lymph node exhibited histologi c and FISH genomic features of metanephic adenoma.