Fluorescent In-situ Hybridization Study of Non-papillary Oncocytic/Eosinophilic Renal Cell Carcinoma.

Aims: Papillary renal cell carcinoma (PRCC) and clear cell RCC (CRCC) can display extensive areas with oncocytic/eosinophilic changes and may be associated with either minimal papillary architecture. These nonpapillary oncocytic/eosinophilic RCC often mimic renal oncocytoma (RO). We investigated numeric changes of chromosomes 7, 17, and Y and loss of the small arm of chromosome 3 in the above-mentioned oncocytic RCC by using the florescent in-situ hybridization (FISH). Materials and Methods: Archival cases of oncocytic RCC previously screened by immunohistochemical study were submitted for FISH. Results: There were a total of 9 cases out of a total of 650 renal carcinomas surgically resected. Seven tumors displayed an immunoprofile of CRCC or PRCC with RCC(+)/CD117(-) and variable reactivity for CK7 and alpha-methylacyl-CoA racemase. FISH showed trisomies 7/17 with or without loss of Y in 5 tumors. Loss of loci 3p25 and 3p14 was identified in another 2 cases. The remaining 2 carcinomas previously reported as malignant RO owing to cytological atypia and lymph node metastasis showed immunoprofile of RCC(-)/CD117(+) and absence of numeric changes for chromosomes 7, 17, and Y or loss of loci 3p25 or 3p14. Conclusions: In this uncommon variant of RCC, FISH for chromosomes 7, 17, and Y lend more support for the role of immunostaining in distinguishing RO and chromophobe RCC from the nonchromophobe RCC. FISH for chromosomes 7, 17, Y, and loci 3p25 and 3p14, and not immunostaining for alpha-methylacyl-CoA racemase and CK7 is helpful in distinguishing CRCC from PRCC.