MiT family translocation renal cell carcinoma: looking for diagnostic and druggable markers

Renal cell carcinomas with chromosome translocation are rare neoplasms which often occur in young patients. In the last World Health Organization (WHO 2016) are named as MiT family translocation renal cell carcinoma comprising two different entities: Xp11 renal cell carcinoma and t(6;11) renal cell carcinoma. Recently, renal cell carcinomas with TFEB amplification has been described in connection with t(6;11) renal cell carcinoma. We analyzed 30 MiT family translocation renal cell carcinoma and 2 renal cell carcinomas with TFEB amplification collecting data on clinical, histological, immunohistochemical and molecular features. In this study, we sought 1) immunohistochemical diagnostic markers (cathepsin K, CD68 (PG-M1), PAX8) since the differential diagnosis is challenging, especially with pure epithelioid PEComa/epithelioid angiomyolipoma; 2) fluorescence in situ hybridization diagnostic features to reach the correct diagnosis; 3) predictive markers (MET, AXL, VEGF) in tumor tissue for target therapy. Histologically, either cytological or architectural appearance was peculiar in each case. By immunohistochemistry, almost all MiT family translocation renal cell carcinomas expressed PAX8. Staining for cathepsin K was found in 65% of Xp11 renal cell carcinomas, only a few cases were positive for melanogenic markers and all cases were negative for CD68 (PG-M1 clone). All t(6;11) renal cell carcinomas labelled for cathepsin K and Melan-A and negative for CD68 (PG-M1 clone). Seven pure epithelioid PEComa /epithelioid angiomyolipomas, used as control, were positive for cathepsin K, melanocytic markers and CD68 (PG-M1) and negative for PAX8. All MiT family translocation renal cell carcinomas were negative for AXL; 61% of Xp11 renal cell carcinomas and 5 of 7 t(6;11) renal cell carcinomas expressed MET. Fluorescence in situ hybridization results showed the presence of TFEB gene translocation in all t(6;11) renal cell carcinomas and TFE3 gene translocation in all Xp11 renal cell carcinoma with a high frequency of split fluorescent signals (mean 74% and 68% respectively). Among the eight t(6;11) renal cell carcinomas, one case displayed a high level of TFEB gene amplification and two showed increased TFEB gene copy number (3-4 copies of fluorescent signals) with a concomitant increased number of CEP6. Those three cases behaved aggressively. By FISH, VEGFA was amplified in all three cases with TFEB amplification and increased VEGFA gene copy number was observed in the two aggressive cases t(6;11) renal cell carcinomas with an overlapping increased number of TFEB fluorescent signals. Overall, VEGFA mRNA expression was observed in 8 of 10 cases (80%); of these 8 cases, three cases showed high level TFEB amplification, one case showed TFEB rearrangement with increased TFEB gene copy number, while four showed TFEB gene rearrangement without increased copy number. In conclusion, we report the high frequency of split signals by FISH in MiT family translocation renal cell carcinomas suggesting that 40% of split signals could be used as the proper cut-off to reach the correct diagnosis. We demonstrate the usefulness of CD68 (PG-M1) immunohistochemical staining in distinguishing MiT family translocation renal cell carcinoma from pure epithelioid PEComa/epithelioid angiomyolipoma. Finally, VEGF, MET but not AXL may be potential predictive marker for targeted therapy in MiT family renal cell carcinomas.