Cytokeratin 7 and Antimitochondrial Antibody Expressions in the Differential Diagnosis of Renal Epithelial Neoplasms with Eosinophlic Cytoplasm

Objectives: The distinction between epithelial renal tumors with eosinophilic cytoplasm, namely, chromophobe renal cell carcinoma (ChRCC), clear cell (conventional) renal cell carcinoma (ECRCC) with eosinophilic cytoplasm, and oncocytoma may remain questionable in some cases because of overlapping morphologic features. We evaluated cytokeratin 7 (CK 7) and antimitochondrial antibody (AMA) expressions to determine their potential value in distinguishing these tumors. Methods: In this study, 24 renal tumors were included. They consisted of 9 ChRCCs, 11 oncocytomas and 4 ECRCCs. Immunoperoxidase staining for CK 7 and AMA were performed. Results: CK 7 staining: All ChRCCs showed strong cytoplasmic immunoreactivity with conspicuous peripheral accentuation. All ECRCCs and oncocytomas were negative for CK 7. AMA staining: All ChRCCs showed diffuse cytoplasmic, coarse-granular immunostaining with peripheral accentuation. In all ECRCCs, diffuse cytoplasmic was observed with randomly distributed coarse-granular staining. All oncocytomas demonstrated diffuse cytoplasmic, but fine-granular staining. Combined interpretation of CK 7 and AMA stainings: Seven of eight ChRCCs showed combined AMA (+) with diffuse cytoplasmic coarse-granular with peripheral accentuation and CK 7 (+). All oncocytomas were CK 7 (-) and AMA (+). All ECRCCs was also CK 7 (-) and AMA (+) like oncocytomas, but the staining pattern of AMA was randomly distributed, and coarse-granular, rather than fine-granular which was observed in all of the oncocytomas. Conclusion: These results suggest that the combined interpretation of CK 7 and AMA may provide a better approach in the differential diagnosis of renal epithelial tumors with eosinophilic cytoplasm, in addition to the relatively well-known distinctive immunostaining patterns of AMA. [J Interdiscipl Histopathol 2012; 1(1.000): 11-15]