CIC-DUX4 fusion sarcoma is a round cell tumor now considered an entity separate from Ewing sarcoma with a more aggressive clinical course, occurrence in older age, and predilection to soft tissues.
Follow-up available in 22 patients showed a 5-year overall survival of 72%, which was relatively similar to ES (79%, P=0.738) and significantly better than CIC-DUX4 sarcomas (43%, P=0.005) control groups.
On balance, if the following features are seen: (1) a small round blue cell tumor with histomorphology more atypical than that of Ewing sarcoma, (2) cytoplasmic CD99 staining, nuclear WT1 positivity, negative keratin, desmin and myogenin; and (3) EWSR1 rearrangement negative by FISH, then molecular testing for CIC-DUX4 sarcoma should be considered.
Our findings show that CIC-DUX4 sarcomas occur most commonly in young adults within the somatic soft tissues, having a wide spectrum of morphology including round, epithelioid and spindle cells, and associated with an aggressive clinical course, with an inferior overall survival compared with Ewing sarcoma.
Gene-expression profiles of CDS and eMC revealed upregulation of CIC-DUX4 downstream genes such as PEA3 family genes, <i>Ccnd2, Crh</i>, and <i>Zic1</i> IHC analyses for both mouse and human tumors showed that CCND2 and MUC5AC are reliable biomarkers to distinguish CDS from ES.
Here, using analyses of published whole-genome gene expression microarray data, we identify PAX7 as a gene with significantly increased expression in Ewing sarcoma in comparison to CIC-DUX4 round cell sarcoma.
Our series confirms that CIC-DUX4 fusion-positive sarcomas are aggressive tumours with an adverse prognosis, and with clinical, histological and genetic differences from Ewing sarcoma.
CIC-DUX4 round cell sarcoma differs from Ewing sarcoma in that it has more atypical cytologic features and lacks the diffuse membranous CD99 staining pattern characteristic of Ewing sarcoma.
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.