Expression analysis of kidney-specific cadherin in a wide spectrum of traditional and newly recognized renal epithelial neoplasms: diagnostic and histogenetic implications.

Kidney-specific cadherin (Ksp-cad) is a membrane-associated cell adhesion glycoprotein expressed by the distal nephron tubular cells in its later developmental stages. Chromophobe renal cell carcinoma and renal oncocytoma are reported to be variably positive for Ksp-cad with some studies suggesting a discriminatory role for Ksp-cad. Immunoreactivity in other tumors with granular eosinophilic cytoplasm including clear cell and papillary renal cell carcinomas needs to be clearly elucidated and its expression in emerging novel and other unusual renal epithelial neoplasm subtypes including tumors with uncertain histogenesis is not yet known. In this study, we performed a detailed immunohistochemical analysis for Ksp-cad in a broad range of 136 renal epithelial neoplasms. Reactivity with Ksp-cad was observed in the following tumors: chromophobe renal cell carcinoma [23/25 (92%), diffuse (>50% of tumor cells)] positivity and membranous characteristically accentuating the "plant cell-like" histomorphology of the typical (clear) type, renal oncocytoma [15/20 (75%), usually diffuse staining with predominantly membranous accentuation], papillary renal cell carcinoma [5/17 (29%) all focal to moderate, eosinophilic type or type 2-3/7 (43%), basophilic type or type 1-2/10 (20%)], Xp11 translocation carcinoma [1/4 (25%), diffuse positivity] and clear cell renal cell carcinoma [6/36 (17%) all focal, clear cell renal cell carcinoma with prominent eosinophilic cells 1/7 (14%)]. Immunoreactivity was higher when evaluating whole histologic sections than with tissue microarrays for both chromophobe renal cell carcinoma (100% vs. 60%) and renal oncocytoma (100% vs. 55%). No immunoreactivity was observed in mucinous tubular and spindle cell carcinomas (0/23), high-grade collecting duct carcinomas (of Bellini) (0/3), renal medullary carcinomas (0/2), and urothelial carcinomas (0/6). Our study documents the immunoreactivity of Ksp-cad in the range of contemporarily classified renal epithelial neoplasms. The findings argue against the use of Ksp-cad in differentiating chromophobe renal cell carcinoma and renal oncocytomas and further support their relationship to the distal nephron. Ksp-cad may be helpful in distinguishing these two tumor types from clear cell renal cell carcinoma with prominent eosinophilic cells particularly in cases with limited tissue samples (ie, needle core biopsy). In the similar diagnostic setting, caution must be exercised, however, in differentiating chromophobe renal cell carcinoma and renal oncocytoma from the eosinophilic variant of papillary renal cell carcinoma as moderate expression of Ksp-cad may be observed in papillary renal cell carcinoma. The histogenesis of mucinous tubular and spindle cell carcinoma remains debatable as this tumor does not express Ksp-cad, which is highly expressed normally in the thick ascending loop of Henle and the distal convoluted tubules. In conclusion, Ksp-cad is a useful tumor type associated marker for distinguishing chromophobe renal cell carcinoma and renal oncocytoma from the wide range of nonintercalated cell-related adult renal epithelial neoplasms; addition of this marker to a panel comprised of other histologic subtype-associated markers may greatly facilitate histologic subclassification of adult renal epithelial neoplasms.