Use of a Novel FISH Assay as a Diagnostic Adjunct for Extraskeletal Myxoid Chondrosarcoma.
Dali Huang, Julia A Bridge. University of Nebraska Medical Center, Omaha
Background: Approximately 75% of extraskeletal myxoid chondrosarcomas (EMC) are characterized by a recurrent t(9;22)(q22;q12) translocation resulting in the fusion of the EWSR1 gene on chromosome 22 with the NR4A3 gene on chromosome 9. Less frequently, the NR4A3 gene is fused with a different gene partner; cytogenetic variant translocations t(9;17)(q22;q11), t(9;15)(q22;q21) and t(3;9)(q11-12;q22) with associated NR4A3-TAF15, NR4A3-TCF12 and NR4A3-TFG fusions respectively have been described. EMC may be difficult to distinguish from other cartilaginous or myxoid lesions. As a diagnostic aid, we constructed a FISH probe set that can: 1) be performed on formalin-fixed, paraffin-embedded (FFPE) tissue; and, 2) identify potential unusual variant translocations or cryptic rearrangements involving the NR4A3 locus in EMC.
Design: Probe cocktails of selected BAC clones were developed to assess the NR4A3 locus as a break-apart rearrangement. After establishing the specificity of the probes [on normal peripheral blood lymphocytes and 9;22 rearranged EMC metaphase cells], we evaluated cytologic touch preparations or FFPE tissue sections of four cytogenetic and/or molecular cytogenetic characterized EMC specimens using two-color FISH assays. EWSR1 FISH was performed on one EMC case exhibiting a 9;15 translocation.
Results: NR4A3 abnormalities were detected by FISH in all four EMCs. Detection of equivalent split red and green signals in three cases indicated a balanced translocation event involving NR4A3. Loss of one of the proximal NR4A3 probe signals in the remaining EMC case suggested the presence of an unbalanced structural rearrangement. Subsequent EWSR1 FISH on this same case similarly showed loss of only the distal probe signal consistent with the conclusion of the presence of an unbalanced rearrangement [der(22) of the 9;22 translocation] in this case. The FISH findings with this novel NR4A3 FISH probe set were concordant in all four EMCs that also had informative results for EWSR1 FISH or conventional karyotyping.
Conclusions: FISH analysis with this newly designed probe set is a reliable and specific method for detecting all variant translocations involving the NR4A3 gene locus in routinely processed tissue (including FFPE tissue) and it may serve as a useful diagnostic aid in distinguishing EMC from clinicohistopathologically similar lesions.
Monday, February 28, 2011 1:00 PM
Poster Session II # 263, Monday Afternoon