Genetic heterogeneity in the alveolar rhabdomyosarcoma subset without typical gene fusions.
Previous studies of the PAX3-FKHR and PAX7-FKHR gene fusions in alveolar rhabdomyosarcoma (ARMS) indicated that the corresponding fusiontranscripts are not detectable in 20% of ARMS cases. To investigate the genetic features of this ARMS subset, we identified 23 ARMS cases in which PAX3-FKHR and PAX7-FKHR transcripts were not detected by a standard sensitivity reverse transcription-PCR (RT-PCR) assay. Subsequent analysis with a high sensitivity RT-PCR assay identified low-level expression of PAX3-FKHR or PAX7-FKHR in three cases. Analysis with a Southern blot assay for PAX3 and PAX7 rearrangements and a fluorescence in situ hybridization assay for FKHR rearrangements identified three cases with variant fusions in which PAX3 or PAX7 is postulated to be joined to novel genomic loci. In one such case, RT-PCR analysis of candidate partners identified a fusion of PAX3 to AFX, which is highly similar in structure and function to FKHR. Additional fluorescence in situ hybridization analysis identified two cases in which a PAX3-FKHR or PAX7-FKHR genomic fusion is present but is not associated with a fusion transcript detectable by RT-PCR. Finally, our analyses of the PAX3, PAX7, and FKHR loci did not identify rearrangements in >50% of cases, consistent with the possibility that there is a true fusion-negative subset. In summary, our analysis of ARMS cases without characteristic PAX3-FKHR or PAX7-FKHR transcripts identified several genetically distinct subsets including low expression or atypical presentation of standard fusions, variant fusions with other genes, and possibly true fusion-negative cases.
Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA. barrfg@mail.med.upenn.edu
Frederic G
FG
Barr
Stephen J
SJ
Qualman
Michele H
MH
Macris
Natalya
N
Melnyk
Elizabeth R
ER
Lawlor
Donna M
DM
Strzelecki
Timothy J
TJ
Triche
Julia A
JA
Bridge
Poul H B
PH
Sorensen
D001483:Base Sequence; D015139:Blotting, Southern; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins / Q000235:genetics*; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D015321:Gene Rearrangement; D018740:Genetic Heterogeneity; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008969:Molecular Sequence Data; D015514:Oncogene Proteins, Fusion / Q000235:genetics*; D000072041:PAX3 Transcription Factor; D051763:PAX7 Transcription Factor; D051761:Paired Box Transcription Factors; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018232:Rhabdomyosarcoma, Alveolar / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C085126:FOXO1 protein, human; C108803:FOXO4 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D018398:Homeodomain Proteins; D015514:Oncogene Proteins, Fusion; D000072041:PAX3 Transcription Factor; C489409:PAX3 protein, human; D051763:PAX7 Transcription Factor; C497321:PAX7 protein, human; D051761:Paired Box Transcription Factors; D014157:Transcription Factors; C068686:Pax3 protein, mouse