Oncocytoma,
chromophobe renal cell carcinoma (chRCC), and the eosinophilic variant of clear cell RCC (ccRCC) are morphologically similar
tumors with significantly different clinical courses. These renal
tumor subtypes show characteristic structural genetic changes; however, the
mRNA expression patterns of
oncocytoma and chRCC are strikingly similar.
MicroRNAs (
miRNA) are small
RNA molecules that regulate the expression of many genes and have been shown to be useful for
tumor classification and identification. The
miRNA expression was analyzed from
formalin-fixed
paraffin-embedded tissue in 5 cases each of
oncocytoma, ccRCC, papillary RCC, chRCC, and 4 normal kidney tissues using microarrays. Affymetrix single-nucleotide polymorphism arrays were used to detect chromosomal imbalances in each of the
tumors. Eighteen
miRNAs were significantly different among the 4
tumor types. The
microRNA miR-21, a known oncogenic
miRNA, was found to be upregulated in papillary and clear cell
carcinomas. Four
miRNAs could differentiate oncocytomas from chRCCs and the 3 could differentiate papillary RCC from ccRCC, including miR-126, a known vasculogenic
miRNA. Of the 18 differentially expressed
miRNAs, only 2 correlated with copy number changes in the chromosomal region harboring these genes. One
tumor, originally diagnosed as an
oncocytoma by morphology, showed a virtual karyotype and
miRNA expression pattern consistent with chromophobe
carcinoma. Further investigation of the
tumor showed vascular invasion. Our study suggests that
miRNA expression can be used to differentiate the common subtypes of renal
epithelial neoplasms but further validation is necessary. In addition, the lack of correlation between
miRNA expression and virtual karyotype suggests a non-copy-number-related mechanism for
miRNA gene expression regulation in renal
neoplasia.