Adult papillary renal tumor with oncocytic cells : Clinicopathologic, immunohistochemical, and cytogenetic features of 10 cases

We report a series of 10 oncocytic renal papillary tumors, with the aim of determining their clinicopathologic features. All patients were male (median age, 71 years), treated by radical nephrectomy and free of recurrence or metastasis (median follow-up, 62 months). Tumors (median size, 3.3 cm) were intrarenal and well limited, with no extrarenal extension. They consisted of thin, nonfibrotic papillae lined by a single layer of oncocytic cells, with finely granular eosinophilic cytoplasm and round regular nucleus exhibiting central nucleolus (Fuhrman grade II, except for one grade III). Foci of necrosis were present in most cases. All tumors were immunoreactive for alpha-methylacyl-coenzyme A racemase, vimentin, and CD10; 4 expressed renal cell carcinoma antigen and 3 cytokeratin 7. There were a low number of cytogenetic changes in the 5 analyzed cases (median, 4; range, 1-7), with no trisomy 7 or 17. Papillary architecture, necrosis, and immunohistochemical profiles argued against the diagnosis of oncocytoma and suggested our cases to be part of the papillary renal cell carcinoma group. However, the cases were atypical for type 1 papillary carcinoma (due to oncocytic cells and absence of trisomy 17) and for type 2 (due to a good outcome). These results suggest that adult papillary renal tumors with oncocytic cells might be a distinct variant in the papillary renal cell carcinoma group.