Dual colour fluorescence in-situ hybridization to paraffin-embedded samples to deduce the presence of the der(X)t(X;18)(p11.2;q11.2) and involvement of either the SSX1 or SSX2 gene: A diagnostic and prognostic aid for synovial sarcoma

Identification of the t(X;18)(p11.2;q11.2) and the fusion gene products, SY T-SSX1 and SYT-SSX2, associated with a high proportion of synovial sarcomas , has been shown to be a useful diagnostic aid. This study demonstrates the application of dual colour fluorescence in situ hybridization to paraffin- embedded samples to deduce the presence of the derivative X chromosome and also the position of the breakpoint on chromosome X at either the SSX1 or t he SSX2 gene. This used region specific markers from chromosomes X and 18 a nd an optimized protocol involving microwave exposure. Novel and rapid scor ing criteria were validated which circumvented potential problems of nuclea r truncation and defining cell boundaries. This involved blind analysis of two negative sarcoma samples and three synovial sarcomas in which correspon ding frozen material had been previously shown to have the translocation in volving different SSX genes. Six new cases diagnosed as synovial sarcoma we re also analysed; two monophasic and two biphasic case were deduced to have a breakpoint in the SSX1 gene, one monophasic case an SSX2 breakpoint, and one case did not show rearrangement of the region. The ability to analyse formalin-fixed; paraffin-embedded samples in this way has practical implica tions for aiding the diagnosis of difficult cases, recently ascribed progno stic relevance, and allows further retrospective studies to be carried out. The methodology is also applicable to the identification of other tumour s pecific translocations in paraffin-embedded material. Copyright (C) 1999 Jo hn Wiley & Sons, Ltd.