CIC::DUX4 sarcoma: clinical, diagnostic and therapeutic insights into a distinct oncologic entity

CIC::DUX4 sarcomas are aggressive soft tissue tumours that often mimic Ewing sarcoma but are distinct in their molecular and clinical behaviour. We describe a young adult male initially managed for a presumed primitive neuroectodermal tumour, later confirmed to have a CIC::DUX4 fusion-positive sarcoma through fluorescence in situ hybridisation and NGS analysis. Despite initial response to Ewing-like chemotherapy (vincristine, doxorubicin and cyclophosphamide regimen), the disease rapidly progressed with widespread visceral metastases, including lungs, spleen, kidneys and soft tissues, eventually leading to death. This case highlights the diagnostic challenges posed by CIC::DUX4 sarcomas, their poor response to conventional chemotherapy and the need for early molecular characterisation to guide prognosis and management. Increased awareness and tailored therapeutic approaches are critical in improving outcomes for this molecular subtype.