Unclassified renal cell carcinoma: a report of 56 cases.

Study Type - Therapy (case series) Level of Evidence 4 What's known on the subject? and What does the study add? Unclassified RCC represents 0.7-5.7% of renal tumours. Limited reported data from two series suggests that unclassified RCC is an aggressive form of RCC, mainly because most cases are at an advanced stage at presentation, but overall and cancer-specific survival were not significantly different between unclassified and clear-cell RCC in an additional series of 38 patients. Our study of 56 cases of unclassified RCC describes the pathological features that can be applied to predict prognosis on a daily basis. In particular nuclear grade, TNM classification, tumour coagulative necrosis, tumour size, microvascular invasion and 2004 WHO histotype are independent predictors of disease-free and cancer-specific survival. 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.