Renal oncocytoma with loss of chromosomes Y and 1 evolving to papillary carcinoma in connection with gain of chromosome 7. Coincidence or progression?

Hybrid tumors of the kidney are not rare. Previous studies of hybrid renal tumors have been valuable for the understanding of the pathogenesis and progression pathways of renal cell neoplasm. In this paper we describe the morphologic, immunohistochemical, and genetic features of 2 oncocytomas with evolving papillary renal cell carcinoma (PRCC) in a nephrectomy specimen of a 60-year old male. The patient was referred for urologic oncology consultation after the incidental discovery of a renal tumor. Nephrectomy was performed and two separate masses were present grossly. The tumors were stained with hematoxylin and eosin, cytokeratin 7 and vimentin. Genetic studies included conventional metaphase cytogenetics and fluorescence in situ hybridization (FISH). Morphologically, both tumors were oncocytomas with numerous microscopic papillary nests and psammoma bodies. Papillary carcinoma nests were highlighted with cytokeratin 7 and vimentin positivity and were more prominent in the larger tumor. Conventional cytogenetics and FISH demonstrated loss of chromosomes Y and 1 and gains of chromosome 7. We postulate that the PRCC represents a neoplastic progression by the gain of chromosome 7 oncocytoma with -Y and -1.