Papillary renal cell carcinoma with diffuse clear cells and thyroid-like macrofollicular areas.

Papillary renal cell carcinoma may display some unusual morphologic variations, including diffuse oncocytic change not otherwise specified, oncocytic change associated with an inverted nuclear pattern or nonoverlapping low-grade nuclei, low-grade spindle cells, and diffuse clear cells. Tumors comprised predominantly of thyroid-like follicles and inspissated eosoinophilic, colloid-like secretions (thyroid-like follicular carcinoma of the kidney) have been recently recognized. We report herein an unusual renal carcinoma that displayed diffuse clear cells, papillary architecture, foamy histiocytes, psammomatous calcifications, and large areas (approximately 20% of tumor volume) with thyroid macrofollicular-like structures and eosinophilic, colloid-like secretions. The tumor was diffusely positive for alpha-methylacyl-CoA racemase, cytokeratin 7 and CD10, and was entirely negative for CD15, thyroglobulin, thyroid-transcription factor-1, TFE3, and renal cell carcinoma antigen. Fluorescence in situ hybridization using centromeric DNA probes for chromosomes 7, 17, 3, and 3p25 showed gains only in chromosome 7 and no other aberrations. The tumor was accordingly classified as an unusual morphologic variation of papillary renal cell carcinoma. This case affirms the potential for papillary renal cell carcinoma to display a diffuse complement of clear cells, and documents the heretofore unreported finding of large areas of thyroid macrofollicular structures and eosinophilic, colloid-like secretions in this histotype.