Molecular Approaches to Diagnosis in Ewing Sarcoma: RT-PCR.

Ewing sarcoma is an aggressive, poorly differentiated solid tumor that most commonly arises in the bone and soft tissues of adolescents and young adults. It is defined by recurrent chromosomal translocations generating oncogenic fusions between a FET family gene-most frequently EWSR1-and ETS family transcription factors, most commonly FLI1 or ERG. The EWSR1::FLI1 fusion represents the predominant oncogenic event, occurring in approximately 85% of cases, while EWSR1::ERG is identified in about 10% of tumors; the remaining cases harbor rarer fusion variants. Although additional recurrent genetic alterations have been described, they occur at a lower frequency. Consequently, the identification of gene fusions remains central to the diagnosis of Ewing sarcoma. This chapter describes an RT-PCR-based assay that allows for sensitive and specific detection of known fusion genes, enabling rapid and accurate genetic confirmation of Ewing sarcoma diagnosis.