Immunohistochemical analysis of cytochrome C oxidase facilitates differentiation between oncocytoma and chromophobe renal cell carcinoma.

: In this study, immunohistochemical staining pattern of cytochrome c oxidase subunit 1 (CCO1) was investigated in the differentiation of renal oncocytoma (RO) from eosinophilic (EoC) and classic chromophobe renal cell carcinoma (ChRCC). A feature found in ChRCC/EoC but not in RO is the predominance of a perinuclear halo when stained for CCO1. In a cohort of 103 mixed cases including 44 RO, 37 classic ChRCC and 22 EoC, the diagnosis based on this immunohistochemical feature alone was consistent with the previous routine diagnosis in 95.7%. We reached 100% specificity and 81.4% sensitivity of this pattern in ChRCC. Specificity for RO was 93.2% and sensitivity correspondingly 95.5%. We propose a novel and easily interpretable immunohistochemical method for the discrimination of benign RO from certain subtypes of malignant ChRCC. Because of strong similarity in morphology of the 2 entities the diagnosis often cannot be made based on standard histopathology alone. The study describes for the first time the formation of a perinuclear halo in CCO1 immunohistochemistry as a highly specific marker for the diagnosis of ChRCC. We think this method can be a strong amendment for routine diagnostics in renal cell carcinoma.