Parafibromin as a new immunohistochemistry staining to improve pathologic diagnosis of renal oncocytoma: Analysis of 225 renal tumors.

408 Background: Chromophobe renal cell carcinoma (chRCC) and renal oncocytoma (Onc) are two distinct but closely related entities with strong morphologic and genetic similarities. While chRCC is a malignant tumor, Onc is usually considered as a benign entity. Recently, gene expression profiling applied on chRCC and Onc identified new potential markers that may effectively discriminate the 2 pathologic entities, including parafibromin. This work aims at evaluating the diagnostic value of Parafibromin (Pf) immuno staining on a large number of renal tumor samples. Methods: Sixty-three renal clear cell carcinoma (ccRCC), 47 papillary (Pap), 40 chRCC, and 75 Onc were immunostained for parafibromin antibody (1/200; Santacruz Biotechnology), on a tissue micro array. Results: Parafibromin was positive in 38.6% of Onc, vs 5% of chRCC (p < 0.001), with a 95% specificity, and the positive predictive value observed for parafibromin was 94%. For other tumor types, a positive staining for parafibromin was observed in 7...