Renal oncocytoma: diagnostic utility of cytokeratin-containing globular filamentous bodies.

Sixty-six renal cortical epithelial tumors were classified by light and electron microscopy into 18 oncocytomas and 48 renal carcinomas, and their pattern of cytokeratin and vimentin reactivity was evaluated by immunoperoxidase using paraffin-embedded tissue. We found by electron microscopy that most oncocytomas (11 of 15) contain globular filamentous bodies that consist of a complex of intermediate filaments and organelles. These structures were found to correlate on immunohistochemistry with a discrete punctate cytoplasmic pattern of cytokeratin reactivity, provided the antibody preparation contained specificity for cytokeratins 8 and 18. A similar punctate finding was not observed in four oncocytomas nor in the 48 renal carcinomas. Although 11 oncocytomas failed to express vimentin, seven tumors showed focal reactivity restricted to rare individual cells in areas of sclerosis (five tumors) or in cell clusters bordering central scars (two tumors). We conclude that many oncocytomas contain a potentially diagnostically useful punctate pattern of cytokeratin reactivity and that focal vimentin reactively may be observed in otherwise typical oncocytomas, restricted to tumor cells appearing to be undergoing atrophy.