Expression of kidney-specific cadherin in chromophobe renal cell carcinoma and renal oncocytoma

Kidney-specific cadherin (Ksp-cad) recently was proposed to differentiate chromophobe renal cell carcinoma (RCC) from oncocytoma based on a finding of Ksp-cad expression in 97% of chromophobe RCCs but only 3% of oncocytomas. However, another study showed no difference in Ksp-cad immunoreactivity between these 2 tumors. We attempted to evaluate Ksp-cad expression in renal tumors using expression microarrays and immunohistochemical analysis. Ksp-cad messenger RNA (mRNA) levels were examined in 158 renal tumors, including 15 chromophobe RCCs and 15 oncocytomas. Immunohistochemical analysis was performed on tissue microarrays containing 125 renal tumors, including 36 chromophobe RCCs and 41 oncocytomas. Ksp-cad mRNA compared with normal kidney tissue was 89% in chromophobe RCC and 64% in oncocytoma. Furthermore, 31 of 36 chromophobe RCCs and 31 of 41 oncocytomas showed Ksp-cad immunoreactivity. Ksp-cad was present in chromophobe RCCs and oncocytomas at mRNA and protein levels, providing strong evidence that Ksp-cad immunohistochemical analysis cannot be used in differentiating these tumors.