Renal oncocytoma. I. Cytochrome c oxidase in normal and neoplastic renal tissue as detected by immunohistochemistry--a valuable aid to distinguish oncocytomas from renal cell carcinomas.

Using a polyclonal antibody raised against bovine heart cytochrome c oxidase, the occurrence of this mitochondrial marker enzyme has been investigated in 63 kidney tumors (ten renal oncocytomas, 43 renal cell carcinomas and ten tubulopapillary adenomas) as well as in normal renal tissue by an immunoperoxidase method (PAP-technique). The differentiation between renal oncocytomas and mitochondria-rich carcinomas represents a problem of histopathology since these tumors have a different prognosis and require different patient managements. The strong immunoreactivity in renal oncocytomas contrasted with the much weaker reactivity in renal carcinomas and adenomas. Even mitochondria-rich (granular cell type) carcinomas exhibited only moderate staining intensity. Furthermore, single strongly stained oncocytes or small complexes were sometimes detected in normal renal tissue. The demonstration of marked differences in enzyme content between renal oncocytomas and granular cell carcinomas renders this method suitable for unequivocal distinction between these renal neoplasms. The antibody proved to be a valuable marker for detecting "true" oncocytic transformation in renal tumors and was useful in defining even single oncocytes or small oncocytic lesions.