Interphase cytogenetic analysis of distinct X‐chromosomal translocation breakpoints in synovial sarcoma

Synovial sarcomas show a specific translocation involving chromosomes X and 18, t(X;18)(p11.2;q11.2). Two distinct X-chromosomal breakpoints occur in different synovial sarcoma tumour samples. These breakpoints are located within two related genomic regions containing ornithine aminotransferase-like sequences, termed OATL1 and OATL2. Preliminary observations indicated the potential correlation of OATL1-associated breakpoints with biphasic tumours and OATL2-associated breakpoints with monophasic fibrous tumours. The present study uses interphase cytogenetics to investigate the nature of chromosomal aberrations in frozen synovial sarcoma tissue samples. Two-colour fluorescence in situ hybridization (FISH) was performed using probes specific for the centromeres of chromosome X or 18, along with yeast artificial chromosome probes corresponding to the distinct breakpoint regions on Xp. One monophasic epithelial and two monophasic fibrous synovial sarcomas showed an OATL2-associated breakpoint, while a biphasic tumour revealed a hybridization pattern indicating a breakpoint within the OATL1 region. These results confirm our previous suggestion of a relationship between alternative breakpoints in Xp11.2 and different histological phenotypes observed in synovial sarcomas. They also demonstrate the utility of the two-colour hybridization approach for the identification of chromosomal changes in interphase nuclei isolated from frozen tissues.