Oncocytoma

Clinical Futures

·         Most common benign solid renal tumor;

·         Originate from the intercalated cells of the collecting duct;

·         3-7% of all renal tumor, 2-12% multifocal, and 4-14% bilateral;

·         M:F= 2-3:1;

·         Mean patient age is 62-68;

·         10% of cases, oncocytoma and chromophobe RCC may coexist.

Gross Findings

·         Spherical and are large (average size, 7 cm) with a pseudocapsule or no capsule;

·         Cut sections, homogeneously tan-pale yellow, mahogany color;

·         Characteristic fleshy/stellate central scar (33-54%);

·         Necrosis, hemorrhage and calcification may be present.

Microscopic Findings

·         Large cells, granular eosinophilic cytoplasm;

·         Well-defined small nests, no sheet-like arrangement;

·         Nuclei: round/oval/smooth and round, minimal atypia, large nucleoli;

·         Some areas, the nests are separated by a loose hypocellular fibrous stroma.

Differential Diagnosis

Immunohistochemistry Staining

·         Cathepsin H +, EMA+, CK7-scattered strong positive, CD117+

·         RCC-, Vimentin-, CD10-

·         Colloid iron staining: focal positive

Election Microscopy

·         Abundant abnormal mitochondria

Cytogenetics

·         Losses of chromosome 1 and X chromosomes, deletion of chromosome 14 and a balanced translocation involving 11q13.

Treatment and Prognosis

·         Benign tumors, and the prognosis after total or partial nephrectomy is excellent.

Reference

·         http://emedicine.com/radio/topic484.htm

·         AFIP, 4th series

·         Essential of Anatomic Pathology. Liang Cheng. 2nd Edition.