Hybrid Renal Cell Carcinomas Containing Histopathologic Features of Chromophobe Renal Cell Carcinomas and Oncocytomas Have Excellent Oncologic Outcomes

Background: Modern histopathology is able to differentiate chromophobe renal cell carcinomas (cRCCs), oncocytomas, and chromophobe-oncocytic hybrid RCCs; however, the true frequency and clinical courses of these tumors remain unclear. Objective: To determine the clinical course of hybrid RCC. Design, setting, and participants: Ninety-one surgically treated tumors, originally classified as oncocytoma or cRCC, were slide reviewed and reclassified by an experienced uropathologist. Immunohistochemical cytokeratin-7 (CK7) staining was used to distinguish oncocytoma (CK7 positive in < 10% of the cells) and hybrid RCCs (CK7 positive in > 10% of the cells). Interventions: Radical tumor nephrectomy or nephron-sparing surgery. Measurements: Recurrence-free and tumor-specific survival. Results and limitations: Overall, 16 tumors (17.6%) were hybrid RCCs, 32 tumors were cRCCs, and 43 tumors were pure oncocytomas. Perinephric tissue invasion (pT3a) was found in one pure oncocytoma and in two hybrid RCCs. The pathologic stage for cRCC was pT1 in 50% of tumors (n = 17), pT2 in 23.5% of tumors (n = 8), and pT3a in 26.5% of tumors (n = 9). Low-grade RCC was found in 76.5% of tumors (n = 26), and vascular invasion was found in 11.8% of tumors (n = 4). After a mean follow-up of 50 mo, no oncocytomas or hybrid RCCs were found, but two cRCCs had recurred. The 3-yr tumor-specific survival rates for patients with oncocytoma, hybrid RCCs, and cRCC were 100%, 100%, and 97%, respectively. Conclusions: Hybrid RCCs are more common than expected. The survival rate is 100% for both hybrid RCCs and oncocytomas. Hybrid RCCs may be candidates for active surveillance, and surgery may be unnecessary. CRCCs should be treated because a small proportion of these tumors exhibit aggressive clinical courses. (C) 2009 European Association of Urology. Published by Elsevier B. V. All rights reserved.