Diagnosis of uncommon renal epithelial neoplasms: performances of fluorescence in situ hybridization

Renal cell carcinomas (RCC) are divided in several subtypes, characterized by morphological and histological features, protein expression patterns and genetics criteria. The main subtypes include Clear cell renal cell carcinoma (CCRCC), Papillary RCC (PRCC), Chromophobe RCC (ChRCC), oncocytoma, TFE3 and TFEB Translocation renal cell carcinoma (TRCC). In most cases, RCC can be easily classified according to histological criteria and immunohistochemistry. Nevertheless, the subtyping process can be more complex in some cases: differential diagnosis (CCRCC or TFE3 TRCC, PRCC or TFE3 TRCC, oncocytic tumors corresponding to ChRCC or oncocytoma), molecular confirmation ( TFEB TRCC) and unclassified RCC. Complementary analyses are required such as fluorescence in situ hybridization (FISH) for the detection of chromosomal abnormalities associated to each subtype. In this aim, this study assessed the performance of FISH analysis in the histological classification of 359 RCC exhibiting unusual histological characteristics and/or occurring in young people. FISH probes were selected according to the histological features of each tumor. FISH analysis contributed to the histological classification in 73% of the RCC (261/359). Conversely, FISH did not contribute to the diagnosis in 19% of the cases (69/359) and a hybridization failure was observed for the remaining tumors (8%; 29/359). Considering the different RCC subtypes, FISH analysis was highly efficient to confirm the histological diagnosis of CCRCC, PRCC, and TFE3 TRCC and to identify abnormalities of the TFEB gene. However, this strategy showed some limitations for the diagnosis of oncocytic tumors and unclassified RCC, suggesting that additional molecular assays should be evaluated in these cases.