Abstract
Eosinophilic cytoplasm is the most common finding of difficult-to-classify kidney tumors. Morphology, cytogenetics, and immunohistochemical stains are discriminatory. This review compares well-recognized tumors such as granular clear cell carcinoma, papillary variants, chromophobe renal cell carcinoma, and oncocytoma and introduces newly described entities of hybrid oncocytic tumors, carcinomas defined by translocations, and carcinomas with deficiencies in the tricarboxylic acid cycle. The focus is on immunostaining, clinical correlations, and differential diagnoses. Representative examples of some entities are presented with elaboration on their workup. To provide a review of the differential diagnoses for renal neoplasms with eosinophilic cytoplasm and elaborate on methods that may assist with correct identification. Review of current literature on kidney tumors with eosinophilic cytoplasm, as well as the authors' personal experience. Eosinophilic cytoplasm is a feature shared by many kidney tumors. Understanding the morphologic differences and the role of ancillary studies is key when encountering such a tumor.
Highlights
Old and NewContext.—Eosinophilic cytoplasm is the most common finding of difficult-to-classify kidney tumors
This example is thyroidlike follicular carcinoma, which is considered a relative of papillary carcinoma.[9,10]
Up to 90% of cells in oncocytoma and 70% of cells in chromophobe carcinoma have nuclear positivity for progesterone receptor, and both are negative for estrogen receptor.[25]
Summary
Context.—Eosinophilic cytoplasm is the most common finding of difficult-to-classify kidney tumors. Eosinophilic cytoplasm is a well-established feature of oncocytoma and chromophobe carcinoma. This finding is shared by a host of other kidney tumors (Figure 1). Arch Pathol Lab Med—Vol 143, December 2019 inantly oncocytoma/chromophobe RCC-like phenotype, whereas 14% (19 of 136) were clear cell–like, and 13% (18 of 136) resembled papillary RCC, collecting duct sarcoma, or sarcomatoid carcinoma.[3,4] the overrepresentation of eosinophilic tumors among those that are problematic creates an incentive to understand their ISUP classification.[4]. Type 2 papillary RCC and the oncocytic variant share abundant pink cytoplasm and pseudostratified cells. Michalova et al[8] described 10 cases with papillary RCC morphology and immunostaining, but with chromosomal abnormalities resembling oncocytoma. The tumor cells in these specimens were mostly in a single layer, with
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