Expression of kidney-specific cadherin distinguishes chromophobe renal cell carcinoma from renal oncocytoma.

Distinguishing renal oncocytoma from chromophobe and other renal carcinomas is essential, considering their differing biological potentials. Although renal oncocytoma is considered a benign tumor, chromophobe renal cell carcinoma has potentially malignant biological behavior. The numerous reported studies on distinguishing these 2 entities have been based on morphological, histochemical, immunohistochemical, ultrastructural, and cytogenetic features. But none of these features has proven to be reliably specific, especially in tumors with overlapping phenotypes. We report a novel immunohistochemical approach based on the expression of a recently described kidney-specific cadherin (Ksp-cadherin) for the differential diagnosis of these 2 tumors. We compared Ksp-cadherin expression in 212 renal tumors, including 102 clear cell renal carcinomas, 46 papillary renal cell carcinomas, 30 chromophobe carcinomas, 3 collecting duct carcinomas, and 31 oncocytomas. In addition, we examined the expression of epithelial membrane antigen, vimentin, CK7, and Hale's colloidal iron staining. We found that chromophobe renal cell carcinomas consistently (96.7% of cases) demonstrated a distinctive membrane pattern of Ksp-cadherin expression, whereas renal oncocytomas (3.2%), clear cell renal cell carcinomas (0%), papillary renal cell carcinomas (2.2%), and collecting duct carcinomas (0%) usually did not express Ksp-cadherin. CK7 expression was found in 90.0%, 6.5%, 7.8%, 76.1%, and 33.3% of these tumor cases, respectively. Whereas CK7 was detected in different types of renal cell carcinomas, Ksp-cadherin was expressed almost exclusively in chromophobe renal cell carcinomas. Immunohistochemical analysis of Ksp-cadherin offers a fast, reliable approach for the distinguishing between renal oncocytoma and chromophobe renal cell carcinoma that is applicable for routine pathology laboratory studies without the need for time-consuming and costly ancillary studies.