[1073] LMP2: An Immunohistochemical Marker for the Differential Diagnosis of Renal Oncocytoma and Chromophobe Renal Cell Carcinoma Eosinophilic Variant

Gang Zheng, Alcides Chaux, Rajni Sharma, George Netto, Patrizio Caturegli. Johns Hopkins Hospital, Baltimore, MD

Background: LMP2, a subunit of the immunoproteasome, has been reported to be overexpressed in oncocytic lesions of the thyroid gland. In this study, we investigated LMP2 expression in non-thyroidal oncocytic lesions. Renal oncocytoma (RO) and the eosinophilic variant of chromophobe renal cell carcinoma (CHRCC-EV) share similar histological features but differ markedly clinically, but a reliable marker to distinguish the two is lacking.
Design: We selected from the Johns Hopkins surgical pathology archive 36 cases of RO and 49 cases of CHRCC, including 7 CHRCC-EV cases. Immunohistochemical staining for LMP2 was performed on routine and tissue microarray (TMA) sections using a standard protocol. Staining was scored for cellular location (nuclear versus cytosolic), intensity (from 0 to 3), and percent of area involved (from 0 to 100%). An H score was calculated by multiplying the intensity with the extent of the staining signal.
Results: A homogeneous cytoplasmic staining was noted in the majority of both RO cases (30 of 34, 88%) and CHRCC cases (37 of 49, 76%). On the contrary, a significant percentage of CHRCC cases (18 of 49, 37%) showed an appreciable nuclear staining (H score ≥0.1), which was instead only rarely observed in RO cases (2 of 36, 6%, p= 0.001 by chi-squared test).

Importantly, all 7 CHRCC-EV cases showed an appreciable LMP2 nuclear staining (average H score > 1).
Conclusions: LMP2 is expressed cytosolically in the majority of RO and CHRCC cases, but its nuclear expression can be used to distinguish RO from the eosinophilic variant of CHRCC.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 149, Monday Morning


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