Regular articleDiagnostic Utility of Molecular Investigation in Extraskeletal Myxoid Chondrosarcoma

Extraskeletal myxoid chondrosarcoma is characterized by the reciprocal chromosomal translocation t(9;22) and the resultant fused gene EWS RNA-binding protein 1 and nuclear receptor subfamily 4, group A, member 3 (EWSR1-NR4A3). A second cytogenetic rearrangement t(9;17) involves the genes NR4A3 and TAF 15 RNA polymerase II, TATA box binding protein (TBP)-associated factor (TAF15). Less frequent fusion transcript variants of the NR4A3 gene, transcription factor 12 (TCF12)-NR4A3 and TRK-fused gene (TFG)-NR4A3, are associated with t(9;15) and t(9;3) respectively. The samples from 42 patients with extraskeletal myxoid chondrosarcoma were examined for the presence of EWSR1-NR4A3, TAF15-NR4A3, TCF12-NR4A3, and TFG-NR4A3 fusion transcripts by using RT-PCR. Fluorescence in situ hybridization was performed to analyze the status of EWSR1 and NR4A3 genes. The fusion transcripts were detected in 34 of 42 samples (81%); the presence of an EWSR1 or NR4A3 gene rearrangements were detected in 8 of 42 samples (19%) which had tested negative for all fusion transcripts detected by RT-PCR. Of the 34 samples evaluable for fusion transcripts, 23 yielded positive results for EWSR1-NR4A3, 10 for TAF15-NR4A3, and 1 for TCF12-NR4A3. The combination of RT-PCR and fluorescence in situ hybridization on frozen and paraffin-embedded tissue is a sensitive and specific method for molecular detection of recurrent translocations and is an important ancillary method to establish the diagnosis of extraskeletal myxoid chondrosarcoma.