A case ofCIC-rearranged undifferentiated round-cell sarcoma with exclusive spindled morphology and diffuse CD99 positivity: a potential pitfall

CIC-rearranged sarcomas comprise a recognized subset of the so called “undifferentiated small round cell sarcomas” that lack the traditional EWSR1 fusion to one of the ETS family members.1 A smaller percentage have demonstrated BCOR gene rearrangements.2 The CIC gene is most commonly fused with the DUX4 or DUX4L10 genes through t(4;19)(q35;q13) or t(10;19)(q26;q13). An alternative fusion partner, the FOXO4 (Xq13.1) gene, has recently been identified.3 CIC-rearranged sarcomas have a distinct gene signature compared to classic Ewing sarcomas with upregulation of ETS transcription factors and WT1. They are more common in adults, in soft tissue locations as opposed to bone, and they have a mixed response to neo/adjuvant traditional Ewing sarcoma chemotherapy protocols.4 This article is protected by copyright. All rights reserved.