The claudin family of epithelial tight junction proteins that play critical roles for cell-cell adhesion and maintenance of cellular polarity.  Claudin members are expressed in a tissue specific manner; claudin-7 expression is localized to the distal nephron epithelium.  Claudin-7 has been extensively studied in renal cell carcinoma (RCC) subtypes.  By immunohistochemical (IHC) analysis, membranous claudin-7 expression was detected in 67% of chromophobe RCC, compared with 0% of clear cell RCCs, 28% of papillary RCCs, and 23% oncocytomas.    Claudin-7 expression may provide clinical utility in the differential diagnosis of chromophobe RCC and oncocytoma.  While both chromophobe RCC and oncocytoma are derived from intercalated cells of the cortical collecting duct, oncocytomas are typically benign lesions whereas chromophobe RCCs are potentially aggressive malignancies.  These RCC subtypes can be difficult to differentiate by morphology alone.  Hornsby and colleagues examined claudin-7 IHC and reported 71% and 73% positive and negative predictive values for the differential diagnosis of chromophobe RCC from oncocytoma.