Renal Oncocytoma
Satish K. Tickoo, MD
Victor E. Reuter, MD
Key Facts
Etiology/Pathogenesis
Loss of chromosomes Y and 1; Ch 11q13 alterations
Many tumors with normal karyotype
Clinical Issues
Benign
Macroscopic Features
Well circumscribed, nonencapsulated
Mahogany brown to yellow-tan color
Central stellate scar: 33%
Microscopic Pathology
Architecture: Typically solid nests, but micro- and macrocysts or tubules also common
Abundant granular eosinophilic cytoplasm; uniform, round nuclei with vesicular chromatin and frequently prominent central nucleoli
CD117 positive; CK7 usually negative, occasionally focal positive; claudin-7 negative or focal positive
Occasional isolated cells or groups of cells with marked degenerative-appearing hyperchromasia and pleomorphism
Ancillary Tests
EM: Cytoplasm packed with mitochondria
Round nucleus; cytoplasm packed with mitochondria mostly showing lamellar cristae
Top Differential Diagnoses
Chromophobe RCC (eosinophilic variant)
Clear cell RCC (eosinophilic variant)
Epithelioid (oncocytoma-like) AML
RCC, unclassified (oncocytic, low-grade type)
 Renal oncocytoma is typically well circumscribed with tan-brown cut surface. A central scar  is present in about 30% of the tumors. Such scars may also be seen in other low-grade slow-growing tumors. |
 The typical histologic features of renal oncocytoma include solid nests of cells with oncocytic cytoplasm and uniform, round nuclei, in a background of variable, but often loose, stroma. |
TERMINOLOGY
Definitions
Benign, oncocytic renal neoplasms with prominent or exclusive nested architecture and uniform round nuclei
ETIOLOGY/PATHOGENESIS
Molecular Abnormalities
Loss of chromosomes Y and 1
Chromosome 11q13 alterations, including translocations
11q13 alterations often involving CCDN1 gene, with overexpression of gene product cyclin-D1
Mitochondrial DNA (mtDNA) mutations, particularly with losses of genes for respiratory chain complex I
Many tumors with normal karyotype and no known FISH abnormalities
Rare familial cases described; later, many of these found to have Birt-Hogg-Dubé syndrome
CLINICAL ISSUES
Epidemiology
Incidence
6-9% of renal tumors
Age
Mean: 62 years (range: 32-89 years)
Gender
M:F = 2:1
Presentation
Usually asymptomatic, detected on radiologic investigations for unrelated symptoms
Prognosis
Benign
MACROSCOPIC FEATURES
General Features
Well-circumscribed, nonencapsulated, usually solitary mass; sometimes multifocal (17%) and bilateral (4%)
Mahogany brown to yellow-tan color
Central stellate scar in up to 1/3 of cases; usually in larger tumors
Uncommon features: Gross cysts, extension into perinephric fat, or vascular invasion
Size
Mean: 4.4 cm (range: 0.6-15 cm)
MICROSCOPIC PATHOLOGY
Histologic Features
Architecture: Typically solid nests, but micro- and macrocysts or tubules also common
Closely packed nests sometimes imparting solid appearance
Nest separated by distinct reticulum framework
Cells with deeply eosinophilic, granular cytoplasm
Nuclei uniform and round, with vesicular chromatin and frequently prominent central nucleoli
Cytoplasmic clearing rare, usually restricted to areas of scarring
Sometimes cells at periphery of nests, “oncoblasts,” have scant cytoplasm
Occasional isolated or groups of cells with marked degenerative-appearing hyperchromasia and pleomorphism
Stroma hypocellular, often hyalinized
Some tumors with perinephric fat (20%) or vascular (5%) invasion
Predominant Pattern/Injury Type
Neoplastic
Predominant Cell/Compartment Type
Oncocytic
ANCILLARY TESTS
Immunohistochemistry
CD117 and Ksp-cadherin positive; CK7 usually negative to occasionally focal positive; claudin-7 negative or focal positive
Electron Microscopy
Round nucleus
Cytoplasm packed with mitochondria mostly showing lamellar cristae
DIFFERENTIAL DIAGNOSIS
Chromophobe RCC (Eosinophilic Variant)
Nuclear irregularities, with perinuclear halos; variety of growth patterns, including solid and broad alveoli
CK7 is often diffusely positive; microvesicles and mitochondria with tubulovesicular cristae on EM
Clear Cell RCC (Eosinophilic Variant)
Fine arborizing vascularity; nuclear atypia, chromatin irregularities
CA9 and CD10, diffuse membranous positivity
Epithelioid (Oncocytoma-like) Angiomyolipoma
Nuclear pleomorphism is common
Smooth muscle and adipose component
Melanocytic markers HMB-45 and Melan-A(MART-1) are positive
RCC, Unclassified (Low-Grade, Oncocytic Type)
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