Objectives: To evaluate the impact of the category of unclassified renal cell carcinoma (URCC) on survival following nephrectomy. Methods: Patients with clear cell RCC (ccRCC, n = 3048) and URCC (n = 38) were identified. Patients with URCC were matched 4:1 with ccRCC patients based on year of surgery, symptoms at presentation, tumor size, stage, regional lymph node involvement, metastases, grade, coagulative tumor necrosis, and sarcomatoid differentiation. Survival was estimated using the KaplanMeier method and compared between ccRCC and URCC patients using log-rank tests. Results: Patients with URCC were more likely to have regional lymph node involvement (P <.001), higher grade (P <.001), tumor necrosis (P <.001), and sarcomatoid differentiation (P <.001) as compared to patients with ccRCC. Overall survival was not significantly different between URCC and ccRCC patients in either the unmatched (P = .337) or matched (P = .345) cohorts. Cancer-specific survival was significantly worse for URCC patients compared with unmatched ccRCC patients (P = .020). However, this difference was not statistically significant when the URCC patients were compared with the matched cohort (P = .688). Distant metastases-free survival was somewhat worse for M0 URCC patients compared with unmatched M0 ccRCC patients (P = .063), but not in the matched cohort (P = .788). Conclusions: Although URCC is more likely to present with advanced clinicopathologic features compared with ccRCC, no statistically significant differences in outcome were noted after adjusting for these features in a matched analysis.
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