Oncocytic renal neoplasms: Diagnostic considerations

The past 3 decades have seen important changes in the study of renal tumors. The use of traditional cytogenetics and current molecular biology techniques have helped us to understand better the differences between the various tumor types, and have helped to refine the histologic classification of renal neoplasia. For a long time, pathologists have observed the range of cytoplasmic characteristics of renal tumors, including those seen in various benign and malignant tumors. For the purpose of this article, we have included benign and malignant neoplasms that are composed predominantly of cells with an abundance of eosinophilic cytoplasm. The focus of this article is to present a discussion of oncocytic renal tumors that emphasizes histopathologic, immunohistochemical, and other ancillary techniques that are used in the routine diagnosis of the different entities and, underscores the importance of correctly diagnosing these tumors, given the differing prognostic implications. We begin at the benign end of the spectrum by discussing renal oncocytoma, including patients who have multiple tumors, which is referred to as renal oncocytosis. This is followed by chromophobe renal cell carcinoma (RCC), including classic and eosinophilic variants. Subjects of recent controversy in renal oncocytoma and chromophobe RCC also are discussed; these include the theory that renal oncocytoma and chromophobe RCC are at two ends of the spectrum (ie, the same entity seen at different levels of progression). An offshoot of the ‘‘renal oncocytoma–chromophobe RCC connection’’ is the controversial concept of ‘‘hybrid oncocytic tumors,’’ which show the presence of areas that resemble chromophobe