NEAT1-TFE3 and KAT6A-TFE3 renal cell carcinomas, new members of MiT family translocation renal cell carcinoma

Microphthalmia-associated transcription factor (MiT) family translocation renal cell carcinoma harbors variable gene fusions involving either TFE3 or TFEB genes. Multiple 5′ fusion partners for TFE3 have been reported, including ASPSCR1, CLTC, DVL2, LUC7L3, KHSRP, PRCC, PARP14, NONO, SFPQ1, MED15, and RBM10. Each of these fusion genes activates TFE3 transcription which can be detected by immunostaining. Using targeted RNA-sequencing, TFE3 fusion gene partners were identified in 5 cases of TFE3 immunohistochemistry positive translocation renal cell carcinoma. Three cases demonstrated known fusions: ASPSCR1-TFE3, MED15-TFE3 and RBM10-TFE3. However, two cases showed unreported NEAT1-TFE3 and KAT6A-TFE3 fusion transcripts. The NEAT1-TFE3 RCC arose in a 59-year-old male; which demonstrated overlapping morphological features seen in NEAT2(MALAT1)-TFEB t(6;11) renal cell carcinoma, including biphasic alveolar/nested tumor cells with eosinophilic cytoplasm. The KAT6A-TFE3 renal cell carcinoma demonstrated typical morphological features of TFE3/Xp11 renal cell carcinoma including papillae, eosinophilic cytoplasm with focal clearing and abundant psammoma bodies. KAT6A gene fusion was reported in some cases of acute myeloid leukemia, which has not been previously reported in solid tumors. This report highlights the genetic complexity of TFE3 translocation renal cell carcinoma; and RNA-sequencing is a powerful approach for elucidating the underlying genetic alterations.