Diagnostic criteria for oncocytic renal neoplasms: a survey of urologic pathologists

Summary Renal oncocytomaand chromophobe renal cell carcinoma have been long recognized as distinct tumors; however, it remains unknown if uniform diagnostic criteria are used to distinguish these tumor types in practice. A survey was distributed to urologic pathologists regarding oncocytictumors. Responses were received from 17 of 26 invitees. Histologically, more than 1 mitotic figure was regarded as most worrisome (n=10) or incompatible (n=6) with oncocytomadiagnosis. Interpretation of focal nuclear wrinkling, focal perinuclear clearing, and multinucleation depended on extent and did not necessarily exclude oncocytomaif minor. Staining techniques most commonly used included the following: cytokeratin7 (94%), KIT (71%), vimentin (65%), colloidal iron (59%), CD10 (53%), and AMACR (41%). Rare cytokeratin7–positive cells (≤5%) were regarded as most supportive of oncocytoma, although an extent excluding oncocytomawas not universal. Multiple chromosomal losses were most strongly supportive for chromophobe renal cell carcinoma diagnosis (65%). Less certainty was reported for chromosomal gain or a single loss. For tumors with mixed or inconclusive features, many participants use an intermediate diagnostic category (82%) that does not label the tumor as unequivocally benign or malignant, typically " oncocyticneoplasm" or "tumor" with comment. The term "hybrid tumor" was used variably in several scenarios. A slight majority (65%) report outright diagnosis of oncocytomain needle biopsies. The morphologic, immunohistochemical, and genetic characteristics that define oncocyticrenal tumors remain incompletely understood. Further studies correlating genetics, behavior, and histology are needed to define which tumors truly warrant classification as carcinomas for patient counseling and follow-up strategies.