SOLID VARIANTS OF PAPILLARY (CHROMOPHIL) RENAL-CELL CARCINOMA - CLINICOPATHOLOGICAL AND GENETIC FEATURES

Papillary renal cell carcinomas (RCCs) traditionally have been defined histologically as tumors with at least 50% true papillae. However, th ese tumors also have characteristic immunohistochemical and genetic fe atures that separate them from other RCCs. We identified six tumors co mposed of solid sheets of cells without true papillae but that otherwi se resembled papillary RCCs, which we feel represent solid variants of papillary RCCs. All six tumors were primary lesions of the kidney, al l were strongly reactive for epithelial membrane antigen, cytokeratin 7, and callus keratin, and all were negative for the high molecular we ight keratin antibody 34BE12. Four of four tumors tested showed trisom ies for chromosome 7, chromosome 17, or both by either cytogenetic ana lysis or fluorescence in situ hybridization. Four cases were composed of solid sheets of cells containing distinct micronodules that in some cases resembled abortive papillae. The cells composing the micronodul es had abundant eosinophilic cytoplasm, open chromatin, and in some ca ses prominent nucleoli. The intervening cells had similar nuclei, but the amount of cytoplasm was variable. In three of these micronodular c ases, multiple tumors diffusely replaced the kidney; in the fourth cas e two typical clear cell RCCs and a typical papillary RCC were also pr esent in the same kidney, but the micronodular tumor was unifocal. The two remaining cases were solitary tumors consisting of solid sheets o f cells forming ill-defined tubules. These cells had scant clear cytop lasm and small round to elongate nuclei with occasional nuclear groove s but only rare small nucleoli. Limited follow-up has shown no evidenc e of disease in any patient thus far. The differential diagnosis inclu des ''renal adenoma,'' renal adenomatosis, metanephric adenoma, and cl ear/granular cell RCC. We conclude that solid variants of papillary RC Cs lack true papillae but have characteristic histologic, immunohistoc hemical, and genetic features.