病理学系知识库

Background Ewing′s sarcoma/peripheral primitive neuroectodermal tumor (ES/pPNET) is often difficult to distinguish from other small round cell tumors. The EWS-Ets gene fusions that result from chromosomal translocations in this tumor provide potential molecular diagnostic markers. To apply these molecular markers to commonly available archival materials, we evaluated the feasibility of detecting EWS-Ets including EWS-Flil and EWS-ERG fusion transcripts in paraffin-embedded tissues and its diagnostic value for detecting ES/pPNET.

Methods Thirteen paraffin-embedded samples of ES/pPNETs were retrieved from archives. Thirteen cases of other tumors with small round cell features (including rhabdomyosarcoma, neuroblastoma, lymphoma, small cell carcinoma, and desmoplastic small round cell tumor) were used as negative controls. beta-actin and beta(2)-microglobulin were used as internal controls. A nested reverse transcriptase-polymerase chain reaction ( RTPCR)-based assay was performed to detect the EWS-Flil and EWS-ERG fusion transcripts.

Results beta-actin and beta(2)-microglobulin were detected in 10/13 and 13/13 ES/pPNETs, respectively. EWS-Fli1 fusion transcripts were detected in 11 of 13 (85%) ES/pPNETs. Three chimeric transcripts, all EWS-Flil, were detected in ES/pPNET samples. Among 11 EWS-Fli1-positive cases, 7 cases had a type I fusion transcript involving fusion of EWS exon 7 with Flit exon 6, 2 cases had a type H fusion transcript involving EWS exon 7 with Hit exon 5, and 2 cases expressed fusion transcripts involving EWS exon 7 and Flit exon 8. Type I EWS-Fli1 fusion predominated over other types. Fusion types could not be distinguished in the remaining 2 cases. Thirteen negative controls did not show detectable chimeric messages. There was a significant relationship between EWS-Flil fusion transcripts and CD99 expression.

Conclusions Molecular detection of EWS-Flil fusion transcripts in formalin-fixed paraffin-embedded material by nested RT-PCR is feasible and is useful for the diagnosis and differential diagnosis of ES/pPNETs.