[910] Immunohistochemical Analysis of Oncocytic Renal Tumors

Y Wang, EM Genega, S Signoretti, Y Fu. Beth Israel Deaconess Medical Center, Boston; Brigham and Women's Hospital, Boston; Harvard Medical School, Boston

Background: Renal oncocytic neoplasms include oncocytoma (Onc), chromophobe renal cell carcinoma (ChRCC) and oncocytic type of conventional RCC (OnRCC). Due to overlapping morphologic features, classification of these tumors can sometimes be challenging, even in the hands of experienced pathologists. There are scattered reports that using various immunohistochemical markers to help with the differential diagnosis. We have selected a number of these markers and evaluated their usefulness in the differential diagnosis of these tumors.
Design: Forty-five renal oncocytic tumors including 16 classic Onc, 15 ChRCC, 11 oncocytic neoplasms with atypical features (Onc-Aty), and 3 OnRCC were selected. Onc-Aty included a group of tumors with histological features suggestive of oncocytoma but ChRCC or OnRCC could not be excluded based on morphology. Standard immunohistochemical staining using manufacturer's protocols were performed with antibodies to c-kit (CD-117), cytokeratin (CK) 7, epithelial cell adhesion molecule (EpCAM), survivin and Carbonic Anhydrase IX (CA IX). The percentage of positive tumor cells as well as the intensity of staining were evaluated and scored.
Results: C-kit was expressed in 14/15 of ChRCC, 16/16 classic Onc, 8/11 of Onc-Aty and was negative in OnRCC (0/3). CK7 was strongly and diffusely positive in 14/15 of ChRCC; All oncocytomas showed scattered, starry sky pattern of CK7 staining, which was completely different from the diffuse membrane staining seen in ChRCC. One of 11 Onc-Aty showed diffuse CK7 staining. EpCAM was expressed in all but one ChRCC (14/15) with a diffuse membrane staining pattern; while only presented in 4/16 oncocytoma, 3/11 Onc-Aty and none of the three OnRCC. CA IX was only positive in 1/3 OnRCC with membrane staining and negative in all other oncocytic tumors. Survivin was positive in 5/14 ChRCC, 14/16 oncocytoma, 5/11 of Onc-Aty and 1/3 OnRCC with largely nuclear staining and occasional cytoplasmic staining.
Conclusions: A phenotype of diffuse CK7, EpCAM and C-kit staining with negative CA IX strongly favors ChRCC while negative CK7, EpCAM and C-kit favor OnRCC. The scattered, starry sky staining pattern with CK7 seen in oncocytomas and Onc-Aty is quite characteristic and may prove useful in differentiating these tumors from ChRCC and OnRCC. A positive CA IX result basically excludes a diagnosis of Onc or ChRCC. Survivin appears to be of no clinical value at this point.
Category: Genitourinary (including renal tumors)

Tuesday, March 10, 2009 9:30 AM

Poster Session III # 107, Tuesday Morning