Renal oncocytoma and its congeners.

Although the morphologic criteria for separating renal oncocytomas from renal carcinomas with overlapping features are not established completely, the distinction is crucial because of the marked difference in prognosis. Of the 247 renal carcinomas observed at our hospital since 1947, six had sufficient morphologic features of oncocytoma to pose potential difficulty in diagnosis. We term this group the "congeners of renal oncocytoma." Both the congeners and our 10 oncocytomas were well-circumscribed tumors, varied considerably in size, and were composed of cells with granular, pink-red cytoplasm. The congeners lacked the diffuse organoid packeting of cells, characteristic of oncocytoma. Additional features that helped separate individual congeners from oncocytomas included yellow-tan rather than brown-red gross color, necrosis, pleomorphism, ballooned cytoplasm, or clear cells. Our studies indicate that some renal carcinomas have fields identical to oncocytoma, and frozen section, needle biopsy, or aspiration cytology from such an area could lead to a misdiagnosis.