Fluorescence in situ hybridization analysis of extraskeletal myxoid chondrosarcomas using EWSR1 and NR4A3 probes.

Extraskeletal myxoid chondrosarcomas (EMCs) are characterized histologically by a cord-like or lace-like arrangement of small round cells or short spindle cells with eosinophilic cytoplasm distributed in a rich myxoid matrix. Atypical cases of EMC have also been described, with areas of poor mucus production and high cellularity and a transition to typical EMC. Most cases of EMC harbor the chromosomal reciprocal translocation t(9;22) (q22;q12) and the resultant fused gene, Ewing sarcoma region 1-nuclear receptor subfamily 4, group A, member 3 (EWSR1-NR4A3). Other translocations, such as those involving the NR4A3 gene, have also been noted, although these occur at a lower frequency. On this basis, we conducted a fluorescence in situ hybridization (FISH) analysis of 18 cases of EMC in which patients presented with typical or atypical (areas of high cellularity) histologic features of EMC. We used an EWSR1 probe and a newly prepared NR4A3 probe to evaluate the usefulness of FISH in the pathologic diagnosis of EMC. FISH analysis using the EWSR1 or NR4A3 probe showed split signals in 83% (15/18) of the cases, regardless of the presence of typical/atypical histologic features. Gene rearrangement of EWSR1 was noted in 72% (13/18) of the cases, and rearrangement of NR4A3 was noted in 61% (11/18) of the cases. The NR4A3 rearrangement was detected in 2 cases not carrying any EWSR1 rearrangement, as determined by reverse transcription-polymerase chain reaction. These results suggest that FISH analysis of formalin-fixed, paraffin-embedded specimens using EWSR1 and NR4A3 probes is useful and convenient and may provide an ancillary method for the diagnosis of EMC. Copyright 2010 Elsevier Inc. All rights reserved.