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 proto-oncogenic transcription factors ETV1, ETV4 and ETV5. To test the utility of an ancillary diagnostic technique for these tumours, 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 six 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 five of six cases, while ETV5 was positive in six of six. No Ewing sarcoma or other sarcoma tested showed coexpression of these transcripts, while one ETV1/ETV4/ETV5 triple positive previously unclassified round cell sarcoma was identified as harbouring a CIC rearrangement by break-apart fluorescence in-situ hybridization (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 proved to harbour 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.