Dysplastic ("in-situ") Lesions in multofocal renal oncocytomas (oncocytosis)

Preneoplastic lesions for renal oncocytosis have not been well defined. We have attempted to identify the putative in-situ or dysplastic change in nephrectomy specimens with oncocytosis. Cases of multiple oncocytoma previously identified in radical nephrectomy specimens (n = 5) were reviewed for early lesions of renal oncocytosis by light microscopic analysis and by immunohistochemical studies for p53, bcl2 and MIB-1. Microscopic analysis showed that the renal cortical regions in all cases contain isolated groups of tubules partially or completely replaced by oncocytic cells with morphologic features resembling tumor cells in oncocytosis. The oncocytic cells within these tubules are increased in number and are arranged either as solid groups or as single layers in cystically dilated tubules, and may assume a hobnail appearance. They can be distinguished from small foci of oncocytosis as they do not form a coalescent group but are separated in part by intervening normal-appearing tubules. Cytologically, the cells have abundant eosinophilic, granular cytoplasm with a low nuclear/cytoplasmic ratio and demonstrate distinct cell borders. A very characteristic feature of these cells is the retraction space ("windows") between the oncocytic cells. Nuclear features of these cells are not distinctive from normal tubules. Immunostaining with Bcl-2, p53 and MIB-1 antibodies also does not differentiate the putative preneoplastic lesions from normal tubules. Thus, recognition of a putative dysplastic lesion for oncocytosis is possible by routine microscopic analysis. Identification of this lesion in a biopsy or partial nephrectomy specimen should raise the possibility of the existence of renal oncocytosis (multifocality), leading to adequate clinical management.