7.P.37 MOLECULAR METHODS APPLIED TO ARCHIVAL PARAFFIN-EMBEDDED SAMPLES OF EWING’S FAMILY TUMOURS (EFT)

Abstract

Ewing sarcoma is a malignant bone tumour characterized, in 90% of the cases, by the balanced chromosomal translocation t(11;22) which generates a chimeric oncogene that acts as a transcriptional activator. The detection of translocation can be fundamental in cases with an extraosseous or unusual location which are histologically difficult to diagnose and it is also helpful in evaluation of residual disease. We joined immunohistochemical analysis and routine RT-PCR method together, the latter one allowing the detection of the most common fusion transcript EWS-FLI1 in archival paraffine-embedded tissues of EFT patients. We used a pair of primers which allowed us to discriminate between two subtypes of EWS-FLI1 transcript. We selected some sample for EWS-FLI1 typing using a Real-Time PCR assay.

We analysed 54 EFT patients. RNA was extracted from paraffine-embedded sections and reverse transcribed into cDNA. On every sample we performed RT-PCR and immunohistochemistry for the marker CD99; we also selected 5 samples for Real-Time PCR analysis.

Fourty-nine out of 54 samples had a RNA suitable for analysis. Thirty-six patients had EWS-FLI1 type I fusion transcript while 6 patients EWS-FLI1 type II; in 7 samples we couldn’t find any fusion transcript although their RNA was good. We tested 5 of these negative samples with Real-Time PCR and we found 2 patients who were carriers of EWS-FLI1 type I fusion transcript. CD99 resulted positive in 34 samples out of 54.

The detection of fusion transcripts using RT-PCR methods can be useful as a support to EFT diagnosis. Moreover the possibility to assess a Real-Time PCR assay enhances analysis sensibility and minimizes the chance of false positives. EFT cytogenetic characterization completes morphologic and immunophenotipic data allowing a more careful classification and an identification of subgroups with different prognosis.