We performed a detailed immunohistochemical analysis to investigate ETV4 expression in CIC-rearranged undifferentiated round-cell sarcomas and their potential mimics (especially Ewing sarcomas).
By RT-PCR, fusion transcripts involving CIC (19q13) and DUX4 (4q35) were confirmed to be present in both primitive round cell sarcomas, further defining the breakpoints seen by genomic analysis.
As such the WHO classification temporarily grouped the CIC-rearranged tumors under undifferentiated sarcomas with round cell phenotype, until further clinical evidence was available.
In this review we discuss the main categories of undifferentiated round cell sarcoma, in relation to Ewing sarcoma and its molecular variants, with particular emphasis on the genetic and biologic features of recently described entities including desmoplastic small round cell tumor and CIC-DUX4 as well as BCOR-CCNB3-associated round cell sarcomas.
In conclusion, NKX2.2, ETV4 and BCOR IHC may be helpful in daily practice for distinguishing ESFT from CIC or BCOR-associated sarcomas, especially in hospitals without access to molecular assays.
These findings are cautionary regarding use of these immunostains in prospective case workup, whereas the prevalent MYC amplification may represent a therapeutically targetable oncogenic pathway in CIC-DUX sarcomas.
In light of morphologic features that overlap with those of NC from typical anatomical sites we have seen previously, the tumor was best classified as falling within the NC spectrum rather than CIC-associated sarcoma.
A histologic comparison of the CIC-rearranged sarcomas with 20 EWSR1-rearranged Ewing sarcomas showed significantly higher degrees of lobulation, nuclear pleomorphism, the prominence of the nucleoli, spindle cell elements, and myxoid changes in the CIC-rearranged sarcomas.
The spectrum of ELS is now expanding, and additional gene fusion partners besides DUX4 or CCNB3 have been detected, and the terms CIC or BCOR-rearranged sarcomas have recently been proposed.
This case report describes an additional case of <i>CIC-DUX4</i> sarcoma with a novel fusion breakpoint, and demonstrates the value of this next-generation sequencing-based anchored multiplex PCR technique (Archer FusionPlex Sarcoma Panel) in both diagnosis for patient care and in identification of a novel fusion breakpoint in this tumour type.
The diagnosis of sarcoma with CIC-DUX4 gene fusion is difficult in lack of specific pathological characteristics emphasizing the need for molecular analysis.
Heterogeneous elements included a myxoid spindle cell component in three BCOR-CCNB3 sarcomas and an epithelioid cell component in two CIC-associated sarcomas (one CIC-DUX4-positive and one CIC-DUX4-negative sarcomas).