Renal oncocytoma with and without intravascular extension into the branches of renal vein have the same morphological, immunohistochemical and genetic features.

We attempted to investigate the clinicopathological correlation of renal oncocytoma (RO) with renal vein extension. We identified seven ROs with extension into the branches of renal vein. The age of seven patients ranged from 61 to 82 years. Five cases were identified; incidentally, two patients had gross hematuria. After surgery, all patients were alive and free of tumors with follow-up of 1 to 5 years (mean=3.6). Oncocytomas measured from 2.2 to 7.5 cm. Renal vein extension was grossly suspected in 5/7 cases and histologically confirmed in all seven cases. Tumor cells were positive for cytokeratins, mitochondrial antigen, epithelial membrane antigen, and parvalbumin; 5/7 tumors were focally positive for cluster of differentiation 117. Ultrastructurally, the cytoplasm was packed by mitochondria. Molecular genetic analysis did not detect abnormal numbers of chromosomes 1, 2, 6, 7, 10, 17, and XY by fluorescence in situ hybridization, loss of heterozygosity on 3p, and mutation of Von Hippel-Lindau gene in all cases. Array comparative genomic hybridization analysis of two cases did not show any major genetic changes. Conclusions are: (1) renal oncocytomas may have intravascular extension to the branches of the renal vein; (2) renal oncocytomas with intravascular extension to the branches of the renal vein have the same morphological, immunohistochemical, and cytogenetic findings as have their counterparts without evidence of intravascular invasion; (3) the absence of metastases suggests an overall benign behavior of this tumor, but this has to be substantiated by further studies with a long-term follow-up; (4) in a renal tumor with granular cytoplasm showing renal vein extension, it is necessary to carefully exclude renal cell carcinomas (RCC) such as chromophobe RCC, oncocytic variant of papillary RCC, and granular variant of clear cell RCC.