The clinicopathological, ultrastructural, genetic features and diagnosis of small cell variant renal oncocytoma

Report From the International Society of Urological Pathology (ISUP) Consultation Conference on Molecular Pathology of Urogenital Cancers: III: Molecular Pathology of Kidney Cancer

Renal cell carcinoma (RCC) subtypes are increasingly being discerned via their molecular underpinnings. Frequently this can be correlated to histologic and immunohistochemical surrogates, such that only simple targeted molecular assays, or none at all, are needed for diagnostic confirmation. In clear cell RCC, VHL mutation and 3p loss are well known; however, other genes with emerging important roles include SETD2, BAP1, and PBRM1, among others. Papillary RCC type 2 is now known to include likely several different molecular entities, such as fumarate hydratase (FH) deficient RCC. In MIT family translocation RCC, an increasing number of gene fusions are now described. Some TFE3 fusion partners, such as NONO, GRIPAP1, RBMX, and RBM10 may show a deceptive fluorescence in situ hybridization result due to the proximity of the genes on the same chromosome. FH and succinate dehydrogenase deficient RCC have implications for patient counseling due to heritable syndromes and the aggressiveness of FH-deficient RCC. Immunohistochemistry is increasingly available and helpful for recognizing both. Emerging tumor types with strong evidence for distinct diagnostic entities include eosinophilic solid and cystic RCC and TFEB/VEGFA/6p21 amplified RCC. Other emerging entities that are less clearly understood include TCEB1 mutated RCC, RCC with ALK rearrangement, renal neoplasms with mutations of TSC2 or MTOR, and RCC with fibromuscular stroma. In metastatic RCC, the role of molecular studies is not entirely defined at present, although there may be an increasing role for genomic analysis related to specific therapy pathways, such as for tyrosine kinase or MTOR inhibitors.

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

INTRODUCTION

Small-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 METHODS

We 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.

DISCUSSION

Grossly, 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.

CONCLUSION

Small-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.

Identification and Validation of Radiographic Enhancement for Reliable Differentiation of CD117(+) Benign Renal Oncocytoma and Chromophobe Renal Cell Carcinoma

Purpose: The diagnostic differential for CD117/KIT(+) oncocytic renal tumor biopsies is limited to benign renal oncocytoma versus chromophobe renal cell carcinoma (ChRCC); however, further differentiation is often challenging and requires surgical resection. We investigated clinical variables that might improve preoperative differentiation of CD117(+) renal oncocytoma versus ChRCC to avoid the need for benign tumor resection.Experimental Design: A total of 124 nephrectomy patients from a single institute with 133 renal oncocytoma or ChRCC tumors were studied. Patients from 2003 to 2012 comprised a retrospective cohort to identify clinical/radiographic variables associated with renal oncocytoma versus ChRCC. Prospective validation was performed among consecutive renal oncocytoma/ChRCC tumors resected from 2013 to 2017.Results: Tumor size and younger age were associated with ChRCC, and multifocality with renal oncocytoma; however, the most reliable variable for ChRCC versus renal oncocytoma differentiation was the tumor:cortex peak early-phase enhancement ratio (PEER) using multiphase CT. Among 54 PEER-evaluable tumors in the retrospective cohort [19 CD117(+), 13 CD117(-), 22 CD117-untested], PEER classified each correctly as renal oncocytoma (PEER >0.50) or ChRCC (PEER ≤0.50), except for four misclassified CD117(-) ChRCC variants. Prospective study of PEER confirmed 100% accuracy of renal oncocytoma/ChRCC classification among 22/22 additional CD117(+) tumors. Prospective interobserver reproducibility was excellent for PEER scoring (intraclass correlation coefficient, ICC = 0.97) and perfect for renal oncocytoma/ChRCC assignment (ICC = 1.0).Conclusions: In the largest clinical comparison of renal oncocytoma versus ChRCC to our knowledge, we identified and prospectively validated a reproducible radiographic measure that differentiates CD117(+) renal oncocytoma from ChRCC with potentially 100% accuracy. PEER may allow reliable biopsy-based diagnosis of CD117(+) renal oncocytoma, avoiding the need for diagnostic nephrectomy. Clin Cancer Res; 24(16); 3898-907. ©2018 AACR.