Detailed cytogenetic and array analysis of pediatric primitive sarcomas reveals a recurrent CIC–DUX4 fusion gene event

Pediatric undifferentiated soft tissue sarcomas (USTS) are a diagnostically challenging group of neoplasms. Recently, a subcategory of USTS with primitive round cell morphology and a t(4;19)(q35;q13) rearrangement has been defined. The present study applied high-throughput array comparative genomic hybridization together with spectral karyotyping, four-color fluorescence in situ hybridization (FISH), and reverse transcriptase–polymerase chain reaction (RT-PCR) to a series of three pediatric USTS. Two of these had primitive round cell morphology with CD99 positivity; the third had a spindled and myxoid appearance. By genomic analyses, both primitive round cell sarcomas had t(4;19)(q13;q35) rearrangements in addition to several imbalances throughout the genome. Four-color FISH and in silico analyses of the breakpoint region at 19q13 identified the potential involvement of the candidate oncogene CIC. By RT-PCR, fusion transcripts involving CIC (19q13) and DUX4 (4q35) were confirmed to be present in both primitive round cell sarcomas, further defining the breakpoints seen by genomic analysis. Described here are two tumors belonging to the rare category of CIC–DUX4-positive primitive sarcomas, with detailed cytogenetic and genomic information regarding this novel subclass of pediatric malignancy. Molecular and cytogenetic techniques for the detection of the CIC–DUX4 fusion gene are described, to aid in recognition and diagnosis.