Oncocytic renal neoplasms: A molecular approach to a common diagnostic challenge

Oncocytic features are a hallmark of renal oncocytoma (OC) but can be seen in other renal tumors such as clear cell renal cell carcinoma (ccRCC) with granular cells and eosinophilic variant of chromophobe RCC (chRCC). Up to 7% of renal neoplasms are ultimately diagnosed as unclassified RCC with oncocytic tumors accounting for a significant number of these. One of the common diagnostic challenges with renal oncocytic tumors is the differentiation between OC and eosinophilic variant of chRCC. The distinction between these 2 entities is critical due to the prognostic implications and patient management decisions. Immunohistochemistry is generally a useful tool for characterizing many renal tumors but is of limited utility in this situation, since staining patterns for these 2 neoplasms are quite similar. However, OC and chRCC have recurrent chromosomal abnormalities that are characteristic of each tumor type. The use of molecular chromosomal analyses as an ancillary tool for this diagnostic challenge has been reported. This case review focuses on the role of molecular analyses, such as virtual karyotyping with SNP arrays, in the diagnosis of unclassified oncocytic renal tumors.