Unclassified renal cell carcinoma: A report of 56 cases

Objective To evaluate the clinicopathological features and outcomes of 56 patients with unclassified renal cell carcinoma (RCC) meeting 2004 World Health Organization diagnostic criteria. Patients and Methods Urological pathology files of the participating institutions were reviewed and cases of unclassified RCC that met the inclusion criteria were retrieved. Nuclear grade, pT status, tumour size, regional lymph node involvement, distant metastases, coagulative tumour necrosis, mucin and sarcomatoid differentiation were evaluated in radical nephrectomy or nephron-sparing specimens. Significant factors in univariate analysis were then assessed by a multivariate analysis of independent prognostic factors using Cox proportional hazard regression analysis. Results Fifty-six cases met the histological criteria for unclassified RCC. Thirty-four (61%) cases were categorized as unrecognizable cell type (mean overall survival 47 months; median 36 months), 20 (36%) as composites of recognized types (mean overall survival 36 months; median 26 months), and two (4%) (mean survival 16 months; median 16 months) as pure sarcomatoid morphology without recognizable epithelial elements. Cox multivariate analysis showed nuclear grade (P= 0.020), stage (P < 0.001), tumour coagulative necrosis (P= 0.018), tumour size (P < 0.001), microvascular invasion (P < 0.001) and tumour histotype (P= 0.028) to be independent predictors of disease-free survival, with tumour size being the most significant (hazard ratio [HR] 9.068, 95% confidence interval [CI] 3.231-25.453). Nuclear grade (P= 0.026), stage (P < 0.001), tumour coagulative necrosis (P < 0.001), tumour size (P= 0.044), microvascular invasion (P < 0.001), tumour recurrence after surgery (P < 0.001) and tumour histotype (P= 0.056) were independent predictors of cancer-specific survival, with tumour recurrence after surgery being the most significant (HR 14.713, 95% CI 5.329-40.622). Conclusion The prognosis of patients with unclassified RCC seems to be related to clinicopathological features known to be relevant in common forms of RCC. © 2012 THE AUTHORS. BJU INTERNATIONAL © 2012 BJU INTERNATIONAL.