[748] Renal Oncocytomas with Atypical Features: A Clinicopathologic Analysis of 34 Cases

KM Dishongh, CM Quick, N Gokden. University of Arkansas for Medical Sciences, Little Rock, AR

Background: Oncocytomas comprise approximately 5 % of all neoplasms of the renal tubular epithelium. Most occur sporadically with a benign clinical course. Some oncocytomas show atypical histopathologic features, including vascular invasion, perirenal fat infiltration, necrosis, marked nuclear pleomorphism, mitotic activity and focal nests of cells with cytoplasmic clearing/ perinuclear halos (CC/PNH). CC/PNH can be particularly problematic in the differential diagnosis with chromophobe renal cell carcinoma (RCC) and eosinophilic variant of conventional RCC. Classification of such cases in the undetermined malignant potential category has been proposed; however, the existent outcome data are sparse and controversial regarding oncocytomas with atypical features. Here, we evaluated atypical histopathologic features in regards to clinical outcome.
Design: We retrospectively identified 34 oncocytomas in our files and reviewed them to identify cases with atypical features (vascular invasion, perirenal fat infiltration, necrosis, marked nuclear pleomorphism, mitotic activity and focal nests of cells with CC/PNH. Clinical and follow-up data were collected from patient charts and were correlated with histopathological features.
Results: Of the 34 cases, 26 were males and 8 were females. Age range was 52 to 91 years (mean: 70.0 years). Twenty-one tumors were in the right, 12 were in the left kidney. One case was bilateral. Tumor size ranged from 1.0 to16.0 cm (mean: 4.3cm). Four cases (11%) were multifocal. Seventeen cases (50%) had atypical features including 10 cases with PNH resembling, but not diagnostic of, chromophobe RCC, one with focal CC, two with focal papillary areas, seven with marked nuclear pleomorphism, three with perirenal fat invasion and one with focal necrosis. No mitotic activity or vascular invasion is identified. Follow-up was available from 0.5 to 96 months in 30 patients. Only one patient (0.02 %) died of disease at 55 months of initial diagnosis with liver, bone and lung metastases. Focal PNH was the only atypical feature found in this case. Two patients died of unrelated causes. Others, including 17 classical oncocytomas, are free of disease.
Conclusions: Atypical features in oncocytomas are common (50%). Rarely, there is a risk of metastasis to liver, bone and lungs, warranting long-term follow-up. Overall, classical oncocytomas and the great majority (99.98 %) of those with atypical features behave in a benign fashion.
Category: Genitourinary (including renal tumors)

Monday, March 9, 2009 1:00 PM

Poster Session II # 119, Monday Afternoon