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.