The utility of ETV1, ETV4 and ETV5 RNA in-situ hybridization in the diagnosis of CIC–DUX sarcomas

Aims A recently characterized group of undifferentiated small round cell sarcomas harbours fusions of the genes CIC and DUX4. Studies report a distinctive gene expression profile for these sarcomas, including expression of E26 transformation specific (ETS)-family protooncogenic transcription factors ETV1, ETV4, and ETV5. To test the utility of an ancillary diagnostic technique for these tumors, we evaluated chromogenic RNA in situ hybridization assays for ETV1, ETV4, and ETV5, as diagnostic adjuncts for this emerging group of highly malignant sarcomas. Methods and Results We tested 6 confirmed CIC-DUX4 sarcomas and 105 lesions in the differential, including 48 Ewing sarcomas for expression of ETV1, ETV4, and ETV5, scoring expression utilizing a previously validated scale. ETV1 and ETV4 were positive in 5/6 cases, while ETV5 was positive in 6/6. No Ewing sarcoma or other sarcoma tested, showed co-expression of these transcripts, while one ETV1, ETV4, ETV5 positive previously unclassified round cell sarcoma, was identified as harboring a CIC rearrangement by break-apart FISH. Conclusion We identified overexpression of ETV1, ETV4, and ETV5 transcripts in situ in CIC-DUX4 sarcomas using a robust assay in routine archival sections. One previously unclassified round cell sarcoma showed ETV1/4/5 positivity, and was proven to harbor a CIC rearrangement by break-apart FISH. The sensitivity and specificity observed with our in situ hybridization assay implies potential utility as an ancillary diagnostic technique, particularly when faced with limited biopsy samples. This article is protected by copyright. All rights reserved.