Papillary renal cell carcinoma. Histology and immunohistochemistry

Papillary renal cell carcinoma (RCC) is an uncommon subtype of RCC that has distinctive gross, histologic, and cytogenetic features, but for which only limited immunohistochemistry data have been reported. We compared 36 papillary RCCs and five renal cell adenomas with 19 non-papillary (clear cell and granular) RCCs using a variety of antibodies to keratin and carcinoembryonic antigen (CEA). Papillary tumors were often multifocal and associated with coexistent adenomas, whereas nonpapillary tumors generally lacked these features. Low-grade papillary RCCs demonstrated three occasionally overlapping histologic patterns (typical, trabecular, and sclerotic), whereas high-grade tumors were characterized by an admixture of many patterns. Immunohistochemically, 100% (36 of 36 cases) of the papillary tumors were positive for AE1/AE3, and 92% (33 of 36 cases) were positive for callus keratins; only 3% (one of 36 cases) stained for 34BE12, and 11% (four of 36 cases) weakly stained for CEA. The five renal cell adenomas were likewise positive for AE1/AE3 (five of five cases) and callus (five of five cases) keratins. In contrast, 85% (16 of 19 cases) of the nonpapillary tumors stained for AE1/AE3, but only 5% (one of 19 cases) stained for callus; none (0/19) stained for 34BE12, and 10% (2/19) weakly stained for CEA. The consistent expression of callus keratins by papillary RCCs and renal cell adenomas underscores the close relation of these lesions, providing additional evidence for their oncological distinction from nonpapillary RCCs.