[979] Unclassified Renal Cell Carcinoma: Clinico-Pathologic and Immunohistochemical Analysis

A Shukla, J Carvalho, RB Shah, LP Kunju. University of Michigan, Ann Arbor, MI

Background: Renal cell carcinoma, unclassified type (URCC) do not fit readily into any of the clearly described subtypes of RCC. Studies have shown that URCC are usually aggressive carcinomas.Our aims were to assess the spectrum of morphologic and immunohistochemical features of URCC, assess whether a subset of URCC may potentially be re-classified into known subtypes with judicious use of IHC and to identify any adult Xp11.2 translocation RCC.
Design: 30 URCC of 1245 RCC diagnosed between 1998 and 2008 at our institution were retrospectively evaluated. Multiple clinico-pathologic parameters were assessed including age, tumor size, Fuhrman nuclear grade (FNG), pathologic stage, and incidence of documented metastasis. After detailed morphologic assessment, a tissue microarray was constructed and stained with CK cocktail, CK7, AMACR, CD 10, PAX2 CAIX and TFE 3. Expression was characterized as 1 (<10%), 2(weak, 10-50%), or 3 (strong, >50%).
Results: URCC accounted for 2.4% of all RCC, with a mean age at diagnosis of 52 Y (16-83Y) and a slight male predominance (19M:12F). The average tumor size was 9.9cm (1.7-20cm). Majority (18/30, 60%) tumors were FNG 4, while 8 (27%) and 4 (13 %) cases were FNG 3 and 2 respectively. 9 (30%) tumors showed clear cells and papillary architecture, 6 (20%) showed clear cell and chromophobe RCC pattern, 5 were high-grade tumors with solid areas and focal acinar differentiation, 4 had sarcomatoid features mixed with variable clear, hobnail and rhabdoid cells, 3 had tubulocystic pattern with low-grade nuclei and/or oncocytoma like areas and 3 were extensively necrotic with rare papillary areas. 2 (7%) tumors were pT1a, 4 (13%) pT1b, 9 (30%) pT2, 6 (20%) pT3a, and 7 (23%) pT3b, 2 (7%) pT4. Metastasis was documented histologically in 40% cases. UCRCC showed a variable immunoprofile with 72%, 57%, 55% and 37% tumors positive with CD 10, CK cocktail, CA IX and AMACR respectively. Few cases expressed CK 7 and/or PAX2 (17%). No tumors strongly expressed TFE3. Overall, 4 (13%) cases could potentially be re-classified into papillary or clear cell type RCC.
Conclusions: URCC are a heterogenous group of tumors; majority are aggressive, presenting with high grade/stage and subsequently develop metastasis. However, a small group of URCC present with low grade and low-stage. A small subset (13%) could potentially be re-classified into known subtypes. Additional confirmatory molecular studies are ongoing. No adult Xp11 RCC were identified in our cohort. Strong CAIX immunoreactivity in a subset of cases may be of therapeutic significance.
Category: Genitourinary (including renal tumors)

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 163, Tuesday Morning


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