Oncocytoma

Common sites:

Gross features:

• solitary
• tan to mahogany brown
• homogenous
• well circumscribed, non-encapsulated
• may be large (up to 12cm)
• central, stellate, radiating scar in 33% (larger lesions)

Histologic features:

• large, densely eosinophilic round to polygonal cells
• solid compact nests, acini, tubules, or microcysts embedded within a hypocellular, often hyalinized stroma
• small, round, benign-appearing nuclei
• evenly dispersed chromatin
• large centrally placed nucleolus
• occasional clusters of cells with pleomorphic and hyperchromatic nuclei
• extension into perinephric fat may be seen
• no necrosis
• mitoses rare

Immunophenotype:

Marker:	Sensitivity:	Specificity:
Hale’s colloidal iron (neg; may be focally diffuse)
CK7 (focal, scattered single cells and small clusters of cells)
Most keratins
EMA
Vimentin (neg or focally positive / scattered clusters)

Molecular features:

•  3 groups cytogenetically:
• Loss of 1 and/or 14 and one sex chromosome (Y most often)
• Rearrangemetns of 11q13
• t(9;11)
• t(5;11)
• heterogenous abnormalities
• both numerical and structural aberrations

Other features: