[Eosinophilic vacuolated tumor of the kidney: clinicopathological and molecular characteristics]

Objective: To study the clinicopathological features, immunophenotype, molecular changes, differential diagnosis and prognosis of eosinophilic vacuolated tumor (EVT) of the kidney. Methods: Four cases were collected retrospectively from 2014 to 2020 at Ningbo Diagnostic Pathology Center. The clinicopathologic features and immunophenotypic profile were studied by light microscopy and immunohistochemistry. Targeted next-generation sequencing (NGS) panel was used to detect cancer-associated mutation. Follow-up and literature review were also performed. Results: Among the 4 patients studied,2 were males and 2 were females. The age of the patients ranged from 44 to 63 years (the mean age: 51 years).Tumor size ranged from 1.5 to 4.2 cm (mean: 2.3 cm). Microscopically, tumors were well-circumscribed, unencapsulated. Thick-walled vessels and entrapped renal tubules were found within or at the periphery of the tumors. The tumors were predominantly composed of nest pattern, and focal tubular pattern. The tumor cells exhibited abundant, eosinophilic, granular cytoplasm and conspicuous, large nucleoli. Prominent intracytoplasmic vacuoles were seen. These cytoplasmic vacuoles varied in size and frequently coalesced into a large space. Loose fibromatous or hyaline stroma was focally noted. Immunohistochemically, the tumor cells in all cases exhibited a CD117+/CK7-phenotype. All cases were positive for CD10 and p504s. MTOR, S6 and cathepsin K were positive in 4 cases. TFE3, CA9, Melan A and HMB45 were negative in all cases. SDHB retained expression. NGS demonstrated MTOR mutations in all cases, and TSC2 mutation in 2 cases. Conclusions: EVT is a rarely oncocytic renal tumor with unique morphology, immunohistochemical phenotype, molecular profile and an indolent behavior. Recognition of the characteristics of this novel but rare entity will allow for better classification of renal tumors.