[61] Diagnostic Utility of Dual-Color Break-Apart Chromogenic In Situ Hybridization for Detection of Rearranged SYT in Formalin-Fixed Paraffin-Embedded Tissue of Synovial Sarcoma

A Kumagai, T Motoi, K Tsuji, T Imamura, T Fukusato. Faculty of Medicine, Teikyo University, Tokyo, Japan; Teikyo University Hospital, Tokyo, Japan

Background: Synovial sarcoma (SS) consistently carries specific chromosomal translocation t(X;18) and its derivative chimeric genes, either SYT-SSX1 or SYT-SSX2. Detecting these genetic abnormalities by RT-PCR and FISH has been powerful aid for the diagnosis of SS. Recently, chromogenic in situ hybridization (CISH) has gained attention as a newly developed modality that enables simultaneous visualization of both genomic abnormality and the morphology of tumor cells. However, successful use of CISH on the diagnosis of sarcomas has yet to be reported. In this study, we investigated the diagnostic utility of dual-color break-apart CISH as a new method for detecting SYT rearrangement in SS.
Design: Formalin-fixed paraffin-embedded tissue samples (FFPEs) from 12 cases of SS and 9 cases of 4 soft tissue sarcomas from which SS need to be distinguished (non-SS). In order to detect SYT rearrangement in SS, dual-color break-apart probes were customly designed at the region adjacent to SYT, and were labeled with Texas Red and FITC. After interphase FISH assay, subsequent CISH assay was performed on the same section. For detection of SYT rearrangement by CISH and FISH, the numbers of definite split signals were counted in sixty nuclei per sample. SYT-SSX1 and SYT-SSX2 fusion status was examined by RT-PCR using RNA extracted from the same FFPEs. The results of CISH, FISH and RT-PCR were correlated.
Results: Positive split signals of SYT identified by CISH ranged from 17.5 to 79.2 %(mean 55.2%) in SS, while they were not detected in non-SS. By FISH, split signals were present in 17.5 to 65.0%(mean 39.2%) in SS, but negligible in non-SS (range 0-1.7%, mean 0.2%). These results were consistent with the result of RT-PCR, in which SYT-SSX1 was detected in 10/12 (83.3%) and SYT-SSX2 was in 2/12 (16.7%), while fusion genes were not detected in non-SS.
Conclusions: CISH-based SYT rearrangement detection system using FFPE provides a highly sensitive and specific method for diagnosis of SS, with the accuracy comparable to FISH and RT-PCR. CISH has several advantages over the FISH and RT-PCR. It circumvents the difficulty to use complicated fluorescence microscope and the unavoidable signal fading of FISH. Unlike RT-PCR, CISH is readily applicable to the FFPEs without influence of poorly preserved RNA.CISH-based method has a great potential for the routine use on the diagnosis of SS.
Category: Bone & Soft Tissue

Monday, March 9, 2009 1:00 PM

Poster Session II # 27, Monday Afternoon