Eosinophilic solid and cystic renal cell carcinoma and renal cell carcinomas with TFEB alterations: a comparative study

Eosinophilic solid and cystic renal cell carcinoma (ESC RCC) is a recently described renal tumour entity with frequent cytokeratin (CK)20 positivity, commonly harbouring TSC mutations. In contrast, frequency of CK20 expression and presence of TSC mutations are unclear in TFEB-amplified RCC and TFEB-translocated RCC, which frequently express Melan A. Herein, we provide a comparative analysis of six ESC RCC with four TFEB-amplified/translocated RCC.We assessed the frequency of CK20 and Melan A expression by immunohistochemistry and of TSC mutations by next-generation sequencing. TFEB alterations were confirmed by fluorescence in-situ hybridisation (FISH). All tumours showed voluminous eosinophilic cells with granular cytoplasm, prominent nucleoli, and most showed admixture of solid and cystic areas. CK20 expression was found in all six ESC RCC and in all RCCs with TFEB alterations. Melan A positivity was identified in five of six ESC RCC and four of four RCC with TFEB alterations. We found TSC mutations in two ESC RCCs, including in one case also harbouring a CIC fusion, and identified a TSC mutation in one TFEB-amplified RCC.ESC RCC represents an emerging renal tumour entity with some histological, immunohistochemical and molecular overlap to TFEB-amplified/translocated RCC. FISH for TFEB aids in this differential diagnosis in challenging cases.