Is so-called oncocytic papillary renal cell carcinoma a distinct entity? A multi-institutional morphologic, immunohistochemical and fluorescence in-situ hybridization study
Al-Obaidy K, Eble J, Cheng L, Williamson SR, Sakr W, Gupta N, Idrees M, and Grignon D. Is so-called oncocytic papillary renal cell carcinoma a distinct entity? A multi-institutional morphologic, immunohistochemical and fluorescence in-situ hybridization study. Lab Invest 2018; 98:324.
Background: Papillary renal cell carcinoma (PRCC) is the second most common type of RCC. It has been classified into type 1 and 2 based on cytology and architecture. In 2005, a potentially distinct type of PRCC, “oncocytic papillary renal cell carcinoma” was first introduced. However, to date no clear definition and insufficient data has been presented to support its designation as a separate entity. We evaluated the morphologic, immunohistochemical (IHC) and selected chromosomal characteristics of this entity. Design: We retrospectively reviewed the pathologic characteristics of tumors diagnosed as PRCC from 2004-2017. For inclusion, the tumor had to have pure papillary or papillary/tubular architecture and be composed of cells with dense eosinophilic (oncocytic) cytoplasm with apically located nuclei. After application of these criteria, 14 cases (2 biopsies, 5 radical and 7 partial nephrectomies) were identified. IHC studies (CK7, CK AE1/AE3, EMA, MUC1, CD10, CD117, AMACR and vimentin) and FISH chromosomal (7, 17 and 3p) analysis were performed. Results: Patients mean age was 65 years (range 46-80). Eight patients were women and 6 were men. Mean size was 1.6 cm (range 1-3). ISUP nuclear grade was most frequently 2 (n=8), followed by 1 (n=4) and 3 (n=2). All tumors were stage pT1a. All cases had branching papillae with thin fibrovascular cores, lined by low columnar cells with eosinophilic granular cytoplasm, apical nuclei with apical surface blebbing, regular nuclear contours, and in most inconspicuous nucleoli. Tubule formation (n=2) and cytoplasmic vacuoles (n=6) were also observed. 7 resected tumors had a pseudocapsule. Psammoma bodies, necrosis, mitoses and foamy macrophages were absent in all cases. Immunohistochemically, tumor cells were consistently and diffusely positive for AE1/AE3, EMA, MUC1 and CD10 (apical surface). CK7 was diffusely positive in 12 cases, expressed in <5% of cells in 1 case and was negative in 1 case. CD117 and vimentin were uniformly negative. AMACR expression was present in >50% of cells in 3 cases and 10% in 1 case. Trisomy 7 and/or 17 were detected in 36% of cases (n=5). No 3p deletions were detected. Conclusions: The IHC profile with lack of vimentin expression and consistent MUC1 expression is not typical of usual PRCC. The frequency of trisomies is lower than expected in usual PRCC (up to 80% in our hands - data not presented). These findings suggest that so-called oncocytic papillary renal cell carcinoma may represent a unique tumor unrelated to usual PRCC.