Unclassified renal cell carcinoma: an analysis of 85 cases.

OBJECTIVES: To compare cancer-specific mortality in patients with unclassified renal cell carcinoma (URCC) vs clear cell RCC (CRCC) after nephrectomy, as URCC is a rare but very aggressive histological subtype. PATIENTS AND METHODS: Eighty-five patients with URCC and 4322 with CRCC were identified within 6530 patients treated with either radical or partial nephrectomy at 18 institutions. Of 85 patients with URCC, 55 were matched with 166 of 4322 for grade, tumour size, and Tumour, Node and Metastasis stages. Kaplan-Meier and life-table analyses were used to address RCC-specific survival. Subsequently, multivariate Cox regression analyses were used to test for differences in RCC-specific survival in unmatched samples. RESULTS: Of patients with URCC, 80% had Fuhrman grades III or IV, vs 37.8% for CRCC. Moreover, 36.5% of patients with URCC had pathologically confirmed nodal metastases, vs 8.6% with CRCC. Finally, 54.1% of patients with URCC had distant metastases at the time of nephrectomy, vs 16.8% with CRCC. Despite these differences in the overall analyses, after matching for tumour characteristics, the URCC-specific mortality rate was 1.6 times higher (P = 0.04) in matched analyses and 1.7 times higher (P = 0.001) in multivariate analyses. CONCLUSIONS: These findings indicate that URCC presents with a higher stage and grade, and even after controlling for the stage and grade differences, predisposes patients to 1.6-1.7 times the mortality of CRCC.