Small-cell variant renal oncocytoma: Case report on its clinicopathological and genetic characteristics and literature review

Abstract

IntroductionSmall-cell variant of RO is a rare subtype of renal tumor that can be easily misdiagnosed. To date, only 20 cases had been reported, with its genetic alterations largely unknown due to insufficient information. Materials and methodsWe report a case of the tumor with genetic characterization using exome sequencing chip. We also reviewed literature on this lesion to summarize clinicopathological presentation and differential diagnosis of the tumor. DiscussionGrossly, the tumor is yellow to grayish brown, with clear boundary, central scar, or cystic degeneration. Microscopically, small-cell variant RO show scant eosinophilic cytoplasm with small-round nuclei, arranged in small acini and tubules. Nucleoli and necrosis are rarely observed. Immunohistochemically, the tumor is positive for EMA, cytokeratin 18, CD117 and E-cadherin. Genetically, 4745 differentially expressed genes in this tumor, which encode tricarboxylic acid cycle enzymes and are involved in mitochondrial respiratory chain. This result strongly supports the diagnosis of small cell variant of RO. Findings from the molecular genetic analysis of our case suggests that metabolic pathway-related genes (PIK3R5, PI3KCB, PLA2G4E, PLA2G2A, PLA2G6, PLCB4, PLCG2) may be exploited as potential targets for diagnosis and treatment when necessary. These genes may provide new clues for future research. ConclusionSmall-cell variant of RO is considered benign renal neoplasms with good prognosis. A histochemical and immunohistochemical stains assist in diagnosis of this tumor. Definitive diagnosis can help avoid unnecessary total renal nephrectomy. The exact mechanism of Small-cell variant of RO remains to be further investigated.