Unclassified renal cell carcinoma: Clinical features and prognostic impact of a new histological subtype

Purpose: We characterized the histopathological features and clinical behavior of unclassified renal cell carcinoma and compared the prognostic outcome in patients with unclassified and conventional (clear cell) renal cell carcinoma. Materials and Methods: A total of 31 patients with unclassified renal cell carcinoma are included in the kidney cancer database at our institution. Another 317 matched patients with clear cell carcinoma were used for comparing demographic, clinical, pathological and survival data. Results: The incidence of unclassified renal cell carcinoma was 2.9%. At initial diagnosis 29 patients (94%) with unclassified and 264 (83%) with clear cell renal cell carcinoma had metastatic disease (p = 0.143). Compared with the clear cell variety unclassified disease was associated with larger tumors (p = 0.005), increased risk of adrenal gland involvement (25% of cases, p = 0.0001), direct invasion to adjacent organs (42%, p = 0.00001), bone (52%, p = 0.022), regional (52%, p = 0.0042) and nonregional lymph node (41%, p = 0.03) metastases. Nephrectomy was less likely to be attempted or completed in unclassified renal cell carcinoma cases (61%, p = 0.00007). Unclassified histology was a significant indicator for poor prognosis on multivariate analysis (p <0.0001). Median survival in patients with unclassified renal cell carcinoma was 4.3 months. Nephrectomy alone did not confer any survival advantage in these cases (p = 0.1086), while immunotherapy did (p = 0.008). The combination of nephrectomy and immunotherapy yielded improved survival over immunotherapy alone (p = 0.0356) but patients with unclassified renal cell carcinoma were significantly less likely than those with clear cell disease to be eligible for immunotherapy regimens (p = 0.05). Conclusions: Unclassified renal cell carcinoma is associated with distinct and highly aggressive biological behavior, and poor clinical outcome. Whenever feasible, immunotherapy with nephrectomy is warranted.