Solid papillary renal cell carcinoma: clinicopathologic, morphologic, and immunohistochemical analysis of 10 cases and review of the literature

•The article describes authors’ opinion about so-called solid PRCC. In the new World Health Organization 2016 classification, it is mentioned that not only type 1 and type 2 PRCCs exist but that the spectrum of PRCC can be much broader. Solid PRCC is a confusing and rare variant.•The authors described a series of 10 solid PRCCs using morphologic descriptors and immunohistochemical features.•Major part of the article comprised extensive review of English-written literature dealing with solid PRCC and 2 similar renal entities: metanephric adenoma and epithelioid Wilms tumor.•Major differential diagnostic features, as have been shown in our series and based on data from literature, are highlighted.

Solid papillary renal cell carcinoma is rarely reported in the literature, and its tumor characteristics are not entirely compatible with the concept of 2 histological subtypes of papillary renal cell carcinoma (PRCC). Tumor is composed mostly of small compressed tubules and short abortive papillae giving solid appearance of monomorphic epithelial cells with scanty cytoplasm and small nuclei, sometimes mimicking spindle cells, without or with sparse true papillae. It shows immunohistochemical (+ CK7, + EMA, + AMACR) and genetic hallmarks (polysomy/trisomy 7/17, loss of Y) of conventional PRCC. About 53 cases have been described in the literature, with male predominance and age ranging from 17 to 82 years. By available follow-up data, solid PRCC has a favorable clinical course. We describe 10 cases compatible with the diagnosis of solid PRCC. All patients were males age range was from 34 to 70 years, and all but one were pT1 according to TNM 2009. On follow-up, 9 patients were without evidence of disease, and 1 had recurrent tumor. Size of the tumor ranged from 1.4 to 5.5 cm (mean, 3.32 cm). Tumors were well-circumscribed whitish to yellow masses with granular surface. Although solid architecture was a prominent morphologic feature, detailed analysis revealed that the tumors were composed of compressed short abortive papillae and compressed tubules admixed with true solid areas. Well-formed papillae were exceptionally present. All 10 cases were strongly and diffusely positive for CK7 and negative for WT-1. In conclusion, solid PRCC is a rare tumor with an incidence of less than 1% of all renal tumors. In majority of the cases, tumors were composed of tightly compressed tubular structures and short abortive papillae that render a solid morphologic appearance. Immunohistochemical and molecular features do not differ from conventional PRCC. Metanephric adenoma; epithelioid nephroblastoma; and, rarely, mucinous tubular and spindle cell carcinoma and oncocytic variant of PRCC should be considered in the differential diagnosis.