The Ewing Family of Tumors -- A Subgroup of Small-Round-Cell Tumors Defined by Specific Chimeric Transcripts

TLDR

Diagnosing small‑round‑cell tumors is difficult, but Ewing sarcomas and related PNETs are characterized by t(11;22) or (21;22) translocations that generate EWS‑FLI1 or EWS‑ERG hybrid transcripts. The study aimed to assess the diagnostic value of detecting these hybrid transcripts in tumors presenting with Ewing‑sarcoma or PNET features. RNA from 114 tumors was reverse‑transcribed and amplified by PCR using primers specific for the chimeric transcripts. Hybrid transcripts were detected in 95 % of Ewing sarcoma/PNET cases, absent in all 12 non‑Ewing tumors, and present in 6 of 15 ambiguous undifferentiated tumors, indicating that the Ewing family can be defined by a specific, rapidly detectable molecular lesion applicable to fine‑needle biopsies.

Abstract

Precise diagnosis of small-round-cell tumors is often a challenge to the pathologist and the clinical oncologist. In Ewing's sarcomas and related peripheral primitive neuroectodermal tumors, a t(11;22) translocation or a (21,22) rearrangement is associated with hybrid transcripts of the EWS gene with the FLI1 or ERG gene. To investigate the diagnostic implication of this observation, we searched for these hybrid transcripts in tumors from patients with clinical and radiologic features of Ewing's sarcoma or peripheral primitive neuroectodermal tumors.Samples of RNA from 114 tumors were reverse transcribed and subjected to the polymerase chain reaction with primers designed to amplify the relevant chimeric transcripts. All amplified products were sequenced.In-frame hybrid transcripts were observed in 89 cases. A hybrid transcript was found in 83 of 87 cases (95 percent) of Ewing's sarcoma or peripheral primitive neuroectodermal tumors. Samples of RNA from all of 12 tumors that had been proved to be other than Ewing's sarcoma or neuroectodermal tumors had no hybrid transcript. However, 6 of 15 undifferentiated tumors whose type was ambiguous (nonsecreting, poorly differentiated neuroblastoma or undifferentiated sarcoma) contained a hybrid transcript, suggesting that they might have to be reclassified.A subgroup of small-round-cell tumors identified as belonging to the Ewing family of tumors can be defined according to a specific molecular genetic lesion that is detectable by a rapid, reliable, and efficient method. This approach can be applied to small specimens obtained by fine-needle biopsies.