TFE3-rearranged renal cell carcinoma (TFE3-RCC) is a renal parenchymal neoplasm defined by gene fusion between TFE3 and various possible partner genes. Here, we present a 40-year-old female patient with end-stage kidney disease on haemodialysis. She underwent radical nephrectomy after an unsuccessful biopsy for an incidentally diagnosed renal mass. The tumour was encapsulated with a yellow and haemorrhagic cut surface. Microscopically it had a nested, solid and papillary architecture. The cells were mostly epithelioid with voluminous clear to vacuolated cytoplasm. Scattered psammomatous calcifications and focal hyaline eosinophilic material were present. The cells were PAX8, AMACR, Cathepsin K and TFE3 immunopositive. CAIX showed focal expression, while Keratin 7, MelanA and HMB45 were negative. Fluorescent in situ hybridisation (FISH) using break-apart probes for TFE3 and TFEB were negative. However, next generation sequencing identified a RBM10::TFE3 fusion transcript, confirming a diagnosis of TFE3-RCC. RBM10 and TFE3 are neighbouring genes located on the short arm of the X chromosome. Due to the close proximity between RBM10 and TFE3 gene loci, paracentric chromosomal translocations resulting in RBM10::TFE3 fusion may not be recognised using FISH, presenting a diagnostic pitfall in interpreting this assay. Further molecular testing may be required for definitive diagnosis of TFE3-RCC.
Ding et al. (Sun,) studied this question.