Eosinophilic solid and cystic renal cell carcinoma: A case with two novel TSC2 mutations

Eosinophilic solid and cystic renal cell carcinoma (ESC RCC) is a recently identified subtype of renal tumors. Due to its rarity, pathologists currently have a limited understanding of its clinical and pathological characteristics, which increases the risk of misdiagnosis.

In this paper, we present a case of a 21-year-old male diagnosed with eosinophilic solid and cystic renal cell carcinoma that is more common in females. Histologically, the tumor appears solid-cystic at low magnification, featuring polygonal tumor cells with high-grade nuclei and abundant eosinophilic cytoplasm. Eosinophilic or basophilic globules are observable within the cytoplasm. Foamy histocytes are clustered among the tumor cells. The cysts are lined by tumor cells arranged in a hobnail pattern. Immunohistochemistry results indicate the expression of CK20, AMACR, Cathepsin K, PAX8 and MelanA, while CK7, CD117, CAIX, TFE3, and HMB45 are negative. There is no loss of SDHB and FH. Molecular analysis identified c2158A>T and c.1258-2 A>T mutations in the TSC2 gene. The patient was followed up for two months without any disease progression.

By detailing the distinctive morphology, immunophenotype, and molecular traits of this ESC RCC case, we have outlined the histological, immunohistochemical, and molecular features of this new renal tumor type, and reviewed relevant literatures for a comprehensive understanding. Our findings expand current knowledge of ESC RCC and can assist in reducing misdiagnosis.