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The solid variant of papillary renal cell carcinoma, when strictly defined as a tumor in which no true papillae can be identified, is extremely rare, with only a few cases reported in the literature. This tumor is characterized histologically by solid sheets of cells without true papillae; nevertheless, immunohistochemical and genetic analysis supports the classification of this tumor as a variant of papillary renal cell carcinoma. We report a case of solid variant of papillary renal cell carcinoma affecting a young man and provide histologic and clinical follow-up data, adding an additional case of this extremely rare pathology to the literature. In addition, we describe the first case, to our knowledge, of a solid variant of papillary renal cell carcinoma to contain a high-grade (sarcomatoid) spindle cell component.
(Arch Pathol Lab Med. 2010;134:1210-1214)
Papillary renal cell carcinoma (RCC) is an established subtype of RCC with characteristic histologic, immunohistochemical, and cytogenetic features that separate it from other types of RCC. Papillary RCC traditionally has been defined histologically as tumors with at least 50% true papillae.1 Papillary RCC is separated into a type 1 histologic variant, which features papillae lined by a 1- to 2-cell layer of cuboidal cells with scant cytoplasm, and a type 2 histologic variant, which displays papillae covered by a pseudostratified layer of large eosinophilic cells.2 The type 2 histologic variant is typically associated with a worse prognosis. Several subtypes of papillary RCC had been described, including typical, trabecular, tubular, sclerotic, and high-grade papillary RCC, all of which still contain at least 50% papillary architecture.3 Additionally, a solid component of papillary RCC had been described, reported as a solid architectural growth pattern in tumors, which still contained at least 50% true papillae.3 However, in 1997, Renshaw et al1 identified 6 renal tumors composed of solid sheets of cells with foci of ill-defined tubular formation, but without true papillae, that otherwise resembled papillary RCC by immunohistochemical and genetic analysis. Renshaw et al1 concluded that these 6 tumors represented solid variants of papillary RCCs, which lacked true papillae, and the authors more strictly defined the solid variant of papillary RCC to include only RCCs that lack true papillae but that contain the characteristic immunohistochemical and genetic features of papillary RCC. Encountering a minor solid...