Unclassified renal cell carcinoma (RCC): Analysis of clinical and pathologic features.

16044 Background: Unclassified RCC includes a heterogeneous group of tumors not fitting into other histological subtypes, with a highly variable clinical course. Characterization of clinical and pathologic features may assist in management of these patients (pts).,Pathologic data from pts with unclassified RCC were reviewed by a single pathologist. Clinical characteristics, objective response to treatment, progression-free survival (PFS) and overall survival (OS) were examined. Prognostic factors for PFS and OS were assessed by univariable and multivariable analyses.,52 pts with unclassified RCC were identified. All had prior nephrectomy, 56% were female, and the median age was 60 years (range, 37-87). Histologically, 60% (34/52) had clear cell components, 52% papillary components, 42% both clear-cell and papillary components and 25% had sarcomatoid elements. The majority (65%) had localized disease at diagnosis with 82% of these pts remaining disease free at a median follow-up of 20 months (mos; range 2-85 mos). Eighteen percent of the localized group subsequently developed metastatic RCC (mRCC) at a median of 4.9 mos (range 1.9-13.7 mos) after nephrectomy. In the 18 pts with synchronous mRCC, disease sites included retroperitoneal lymph nodes (82%), lungs (41%), liver (36%) and bone (18%). Ten mRCC pts received systemic therapy (sunitinib 6, sorafenib 3, bevacizumab 1) with 1/10 PR, 6/10 stable disease, and 3/10 with progressive disease as their best response. Overall 73% (16/22) of pts with mRCC progressed and 59% have died. Median PFS and OS are estimated as 5.9 and 14.0 months respectively. Larger tumor size (4.1 vs. 7.3 cm, p=0.02) and sarcomatoid differentiation (44% vs. 15%, p=0.02) were more frequent in pts with synchronous mRCC than in localized disease. In mRCC pts, a multivariable analysis demonstrated sarcomatoid differentiation and number of metastatic sites as independent predictors of PFS. For OS, performance status and sarcomatoid differentiation were independent predictors.,Pts with unclassified RCC appear to have a distinct clinical behavior compared to conventional clear-cell RCC with a higher rate of metastatic disease and poorer clinical outcomes. The presence of sarcomatoid elements may be a risk factor in these pts. [Table: see text].