Differential diagnosis of renal tumors with papillary architecture.

Papillary renal cell carcinoma is the second most common malignant renal epithelial tumor and constitutes approximately 15% of renal cell tumors. However, papillary architecture is neither unique to papillary renal cell carcinoma, nor do all papillary renal cell carcinomas show exclusive papillary histology. Many of the nonpapillary renal cell carcinomas with papillary architecture have been recognized only recently. Distinction of these from papillary renal cell carcinoma is essential, as biologic behavior and potential therapeutic options are distinct in many such tumors. Close attention to the cytologic and growth pattern characteristics will allow us to arrive at the proper diagnosis in most cases, although sometimes immunohistochemistry and rarely genetic evaluation may be needed.