[709] Expanding the Morphological Spectrum of Clear Cell Papillary Renal Cell Carcinoma, a Distinct Renal Cell Carcinoma Subtype

H Aydin, L Sercia, C Magi-Galluzzi, M Zhou. Cleveland Clinic, Cleveland, OH

Background: Clear cell papillary renal cell carcinoma (CCPRCC) is a recently described histological subtype of renal cell carcinoma (RCC) with distinct morphological and immunohistochemical profile (Cheng et al, AJSP, 2008). The tumor typically consists of a mixture of cysts and papillae lined with clear cells. The tumor cells express cytokeratin 7 (CK7) and CA9, but not AMACR, and lack cytogenetic changes characteristic of clear cell and papillary RCC. We report 12 cases of CCPRCC with typical morphological features. However, they also have other unusual patterns, the presence of which may lead to misclassification of these cases as clear cell RCC.
Design: RCC cases were classified as CCPRCC based on their characteristic morphological and immunohistochemical features, namely, cysts of variable sizes mixed with tubules and papillae lined with cells with clear cytoplasm. All the tumor cells were positive for CK7 and CA9 and negative for AMACR. All the cases were stained for CK7, CA9, AMACR and TFE3. Fluorescence in situ hybridization was performed with centromeric probes for chromosomes 7 and 17.
Results: 12 CCPRCC affected 7 men and 5 women with a mean age of 60 years (range 32-78). One patient had bilateral multiple CCPRCC. One patient had diabetic nephropathy. The mean tumor size was 2.0 cm (range 1.3-4.5). Fuhrman grade was 1 in 5, 2 in 6 cases, and 3 in 1 case. The stage was T1a in 10, and T1b in 2 cases. Compressed tubules interspersed with branching tubules were present in 6, cysts of variable sizes in 10, papillae in 8. CCRCC-like area with clear cell nests separated by fine vascular septa were detected in 10 cases. CCRCC-like tumor cells had clear cytoplasm and low grade nuclei. Immunohistochemically, tumor cells lining the cysts and papillae were positive for CK7 and CA9, but negative for AMACR. The clear cells in CCRCC-like areas were positive for CK7 (10/10) and CA9 (6/9), but negative for AMACR. TFE3 was negative in all the cases. None of the cases had chromosomal gain involving 7 and 17.
Conclusions: In addition to the typical morphological pattern (cysts and tubulopapillae), clear cells nests of variable sizes resembling CCRCC can also be present in CCPRCC. These CCRCC-like areas are immunohistochemically identical to other tumor cells in CCPRCC. The presence of CCRCC-like areas in an otherwise typical CCPRCC should not lead to erroneous diagnosis of clear cell RCC.
Category: Genitourinary (including renal tumors)

Wednesday, March 11, 2009 1:00 PM

Poster Session VI # 129, Wednesday Afternoon