[913] Histomorphological Features in Oncocytic Tumors That May Prevent Their Classification as Renal Oncocytoma

Sana Jadallah, Hongying Huang, Ying-Bei Chen, Anuradha Gopalan, Hikmat Al-Ahmadie, Samson Fine, Victor Reuter, Satish K Tickoo. Memorial Sloan-Kettering Cancer Center, New York, NY

Background: Renal oncocytomas are benign tumors composed of polygonal to round cells with densely granular eosinophilic cytoplasm, a small round uniform nucleus with evenly dispersed chromatin, and arranged in solid compact nests, acini, tubules or microcysts, as defined by WHO. Tumors deviating from such strict criteria have been called RCC unclassified, low grade oncocytic type, oncocytic renal neoplasms of low/unknown malignant potential or renal epithelial oncocytic neoplasms, among others, in the literature. We performed a detailed morphologic review of oncocytomas and oncocytic tumors to determine the morphologic features that result in exclusion of such borderline cases from the category of renal oncocytoma by some pathologists.
Design: 65 cases between 2002-2004, bearing the words oncocytoma or oncocytic in the final diagnosis were reviewed by a dedicated group of uropathologists. Cases reported as eosinophilic variant of chromophobe RCC were not included. Based on consensus, the cases considered as definite oncocytoma and definitely not oncocytoma were excluded from the cohort; the remaining cases with no consensus (oncocytoma vs not oncocytoma) were studied in greater detail, and form the substrate for this study. The morphologic features that prevented considering such cases as not oncocytoma by some were noted in each case.
Results: 40 cases showed the classic morphologic features of oncocytoma and 9 were regarded as not oncocytoma by consensus. No consensus between oncocytoma vs not oncocytoma could be reached in 16. The reasons for not oncocytoma decision were: nuclear irregularities beyond the WHO definition in 15 cases; non-classical growth patterns in 8 [presence of areas with single cells (4 cases) or cribriform architecture (1); trabecular architecture (1); solid growth characterized by sheets of cells (2)], and cellular, desmoplastic stroma associated with thick capsule in 1. Some tumors showed a combination of these non-classical features.
Conclusions: - Nuclear irregularities, architectural features (solid/trabecular/single cells/cribriform patterns), stromal desmoplasia, or presence of thick capsule are the main reasons for (non-chromophobe) oncocytic tumors to be excluded from the diagnosis of renal oncocytoma.
- Because of the consequent designations, such lesions may often be regarded as at least potentially malignant.
- Such tumors define a group that requires further investigations, possibly at the molecular level, to establish whether they are variants of oncocytoma and thus benign, or altogether another entity.
Category: Genitourinary (including renal tumors)

Tuesday, March 5, 2013 1:00 PM

Poster Session IV # 195, Tuesday Afternoon

 

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