Overexpression of bcl-2 protein in synovial sarcoma: a comparative study of other soft tissue spindle cell sarcomas and an additional analysis by fluorescence in situ hybridization

Abstract

The expression of bcl-2 protein was analyzed in 19 synovial sarcomas and 29 additional soft tissue spindle cell sarcomas as controls by the immunohistologic staining of paraffin-embedded specimens; 15 of 19 (79%) synovial sarcoma cases were positive, but all other spindle cell sarcomas were negative including 20 leiomyosarcomas, 4 malignant peripheral nerve sheath tumors, and 4 fibrosarcomas. In 4 cases of bcl-2-positive synovial sarcoma (3 biphasic and 1 focally glandular type), bcl-2 protein staining was much stronger in the spindle cells than in the epithelial cells. A fluorescence in situ hybridization (FISH) analysis with centromeric and whole chromosome painting probes for chromosome 18 and X was performed on 7 synovial sarcomas. The six cases of bcl-2-positive synovial sarcoma consisted of five cases with the t(X; 18) and one case with tetrasomy of chromosome 18 and X. It has been speculated that bcl-2 protein expression is caused by the 14; 18 translocation and other abnormalities of chromosome 18. This study thus showed the feasibility of such a correlation between bcl-2 protein expression and the characteristic cytogenetic abnormality in the synovial sarcoma-X; 18 translocation. In addition, bcl-2 protein also appears to be a characteristic marker of synovial sarcoma and is thus considered to be potentially useful in distinguishing synovial sarcoma from other spindle cell sarcomas.