A Collision Tumor of Papillary Renal Cell Carcinoma and Oncocytoma Case Report and Literature Review

Objectives: The most common renal neoplasms include clear cell, chromophobe, and papillary renal cell carcinomas (PRCCs) and oncocytomas. While lesions containing hybrid features of different tumor types, such as hybrid oncocytic tumors, have been well documented in the literature, the finding of a collision tumor of two distinct tumor types PRCC and oncocytoma is extremely rare. Methods: We present a case of PRCC associated with an oncocytoma. Our discussion includes a review of the available literature on this rare type of collision tumor. Results: Prosection of a partial nephrectomy performed in a 78-year-old man for painless gross hematuria and nocturia revealed a 6.4 x 5 x 3.6-cm well-delineated orange to yellow-tan mass harboring a white-tan 1 x 0.9 x 0.9-cm mass. Histologic diagnosis of PRCC associated with an oncocytoma was rendered By immunohistochemistry, focal CK7 expression was present in the oncocytoma, while strong diffuse positive CK7 expression was present in the PRCC component. Fluorescence in situ hybridization (FISH) revealed trisomy 17 in 39.3% of PRCC tumor nuclei but no significant chromosomal aberration in oncocytoma. Conclusions: In view of this and previously reported cases, thorough sectioning and examination, especially in large oncocytomas, is recommended to exclude the presence of an associated malignancy. To our knowledge, trisomy 17 by FISH has not been previously reported in these extremely rare tumors.