Connective Tissue Oncology Society

2001 CTOS Annual Meeting Posters— Biology

MOLECULAR GENETIC CHARACTERIZATION OF FUSION GENES IN EXTRASKELETAL MYXOID CHONDROSARCOMAS
I Panagopoulos¹, F Mertens¹, N Mandahl¹, O Brosjö², S Heim³, B Bjerkehagen³, R Sciot⁴, P Dal Cin⁵, J A Fletcher⁵, C D Fletcher⁵
¹Dept of Clinical Genetics, Lund University, ²Dept of Orthopedics, Karolinska Hospital, ³The Norwegian Radium Hospital, ⁴Dept of Pathology, ⁵Dept of Pathology, Brigham and Women's Hospital

OBJECTIVE: Extraskeletal myxoid chondrosarcoma (EMC) is a soft tissue neoplasm cytogenetically characterized by t(9;22)(q22;q11-12), generating a hybrid EWS/CHN gene, or a t(9;17)(q22;q11), resulting in an RBP56/CHN chimera. Prior to the present study, only 24 EMCs had been analyzed for the fusion transcripts, and the expression of the native CHN gene had been examined in only two cases. The aim of the present study was to characterize the fusion transcript in 18 cases, and to correlate the findings with karyotypic data.

METHODS: The study was based on 18 surgical biopsies (17 from primary lesions, one from a metastasis) from 18 patients (15 men, three women; age at diagnosis 35-79 years) with EMC.RT-PCR was carried out for the detection of the EWS/CHN and RBP56/CHN chimeric transcripts as well as for the expression of the full length transcript of CHN and the two additional CHN transcript variants: the 3´-end truncated mRNA form and the Nor1b variant with the alternative 5´-untranslated region. Cytogenetic analysis was performed after short-term culturing.

RESULTS: Chromosomal aberrations were detected in 16/17 cases in our series; 13 with involvement of 9q22 and 22q12, and three with rearrangements of 9q22 and 17q11. Fifteen cases carried an EWS/CHN fusion transcript and three an RBP56/CHN transcript. The most frequent EWS/CHN transcript (10 tumors), was fusion of exon 12 of EWS with exon 3 of CHN (type 1), followed by fusion of exon 13 of EWS with exon 3 of CHN (two cases; type 5). In tumors with RBP56/CHN fusion, exon 6 of RBP56 was fused to exon 3 of CHN. RT-PCR analysis of the native CHN showed that it was expressed in 11 tumors, nine of which expressed both the long and short 3´ terminals, with and without the ligand domain, respectively.

CONCLUSION: From the distribution of secondary chromosomal abnormalities and previous in vitro studies of the EWS and RBP56 genes, one might predict that type of chimeric transcript is of biologic significance. Indeed, in the present study, all four patients who developed metastases had tumors with EWS/CHN fusions.