Eosinophilic Vacuolated Tumor of the Kidney: A Review of Evolving Concepts in This Novel Subtype With Additional Insights From a Case With MTOR Mutation and Concomitant Chromosome 1 Loss

Recent advances in molecular genetics have expanded our knowledge of renal tumors and enabled better classification. These studies have revealed that renal tumors with predominantly “eosinophilic/ oncocytic” cytoplasm include a number of novel biologic subtypes beyond the traditionally well recognized renal oncocytoma (RO) and eosinophilic variant of chromophobe renal cell carcinoma (ChRCC). Herein, we present a comprehensive review of Eosinophilic Vacuolated Tumor (EVT), a recently described novel renal epithelial tumor subtype. Leveraging the comprehensive study of radiology, histopathology, electron microscopy and next generation sequencing of a patient with EVT with sporadic MTOR mutation, we shed insight on the pathogenesis of EVT. These data allows us to postulate that loss of chromosome 1 loss observed in EVT with MTOR mutation may be related to mTORC1 being a dimer since a heterodimer of wild-type and mTOR p.L2427R proteins may not confer sufficient mTORC1 activation. mTORC1 is best known for its role in promoting protein translation. Consistently, dilated cisterns of rough endoplasmic reticulum (ER) were noted on electron microscopic examination that likely corresponded to the cytoplasmic vacuoles seen by light microscopy. This ER expansion may contribute to the increase in phospho-S6 observed in these tumors, as S6 is a ribosomal protein and ribosomes may be increased with the ER expansion. We further discuss the evolving concepts in the classification of this emerging entity.