Synovial sarcoma: an immunohistochemical study.

The immunohistochemical staining pattern of 18 cases of synovial sarcoma with two epithelial-specific monoclonal antibodies is described. This is compared with normal synovium, cases of giant cell tumour of tendon sheath (benign synovioma) and a variety of spindle celled sarcomas. Sixteen cases of synovial sarcoma showed staining of the epithelial component with at least one antibody. No staining was seen in normal synovium or in giant cell tumours of tendon sheath. A small number of malignant schwannomas contained groups of cells which stained positively whilst other spindle cell sarcomas either did not stain or showed 'cross-reaction' type staining only. These results add weight to the proposition that synovial sarcomas do not arise from normal synovium, despite their morphological similarities, but from mesenchymal connective tissue. It is also shown that immunohistochemical staining with anti-epithelial antibodies will emphasize the biphasic pattern of synovial sarcomas allowing their distinction from other sarcomas.