DUX4 and Ewing sarcoma: The most frequently observed CIC-rearranged protein involves a fusion between the transcriptional repressor, CIC, and the double homeobox 4 gene, DUX4. Subsequent to their initial description, the World Health Organization (WHO) classified CIC::DUX4 sarcoma (CDS) as a “Ewing sarcoma-like” tumor based primarily on their morphological similarities to Ewing sarcoma (ES).