CIC-DUX4 Fusion-Positive Round Cell Sarcomas of soft tissue and bone: a single institution morphologic and molecular analysis of 7 cases

Abstract

Aims

Round cell sarcomas lacking specific translocations represent a diagnostic challenge. The aim of this study is to describe seven cases of CIC-DUX4 positive sarcomas, including the first reported example arising primarily in bone.

Methods and results

Patients ranged in age from 15 to 44 years (median: 33). Six cases arose from the soft tissues and one from the iliac bone. Morphologically, all cases showed an undifferentiated round cell population with greater atypia and pleomorphism than Ewing sarcoma. Immunohistochemically, all tumours showed focal and weak positivity for CD99 and 5/7 displayed nuclear and/or cytoplasmic positivity for WT1. Five patients had lung metastases at presentation. All patients received chemotherapy according to Ewing sarcoma protocols. All but one patient (the one with a bone tumour) died of disease after a mean of 14.5 months from the diagnosis (range: 8-20 months).

Conclusions

Our series confirms that CIC-DUX4 positive sarcomas are aggressive tumours with an adverse prognosis and with clinical, histological, and genetic differences compared to Ewing sarcoma. The best therapeutic approach needs to be investigated.

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