Recent developments in eosinophilic renal neoplasms: what's new, true and important?

We focus in this review on the latest developments on several eosinophilic renal entities, aiming to provide an update on this topic that was previously addressed by the Genitourinary Pathology Society in their consensus papers on existing renal entities, and on novel, emerging, and provisional renal entities, and in the World Health Organization 2022 Classification of Renal Cell Tumours (5th Edition). The scope of this review includes an update on more recently described eosinophilic renal entities, including low-grade oncocytic renal tumour (LOT), eosinophilic vacuolated tumour (EVT), folliculin (FLCN) mutated tumour, succinate dehydrogenase (SDH)-deficient renal cell carcinoma, epithelioid angiomyolipoma/epithelioid PEComa (eAML/ePEComa), eosinophilic solid and cystic renal cell carcinoma (ESC RCC), anaplastic lymphoma kinase (ALK)-rearranged RCC, fumarate hydratase (FH)-deficient RCC, papillary renal neoplasm of reversed polarity (PRNRP), tubulocystic RCC (TC-RCC), and thyroid-like follicular carcinoma of kidney (TLFCK). These renal entities fall within the spectrum of eosinophilic renal tumours, in addition to the more common ones with eosinophilic features that will not be covered in this review, such as clear cell renal RCC, papillary RCC, chromophobe RCC, TFE3 rearranged RCC, and TFEB-altered RCC. Pathologists need to consider these less common renal entities in the differential of any eosinophilic renal tumour to be able to diagnose them for the benefit of their patients. The recent developments and acquired knowledge on newer renal entities with eosinophilic cytoplasm opened insights into the clinical, pathological, immunohistochemical, molecular, epidemiological aspects, and the prognosis of these entities. We emphasize the role of routine morphology, aided by appropriate and select immunohistochemistry, as essential keys for diagnosing eosinophilic renal tumours.