Immunohistochemical analysis of extracellular matrix components in synovial sarcoma

Little attention has been paid to the composition of the extracellular matrix in synovial sarcoma, a tumour showing both epithelial and mesenchymal phenotypes. As extracellular matrix participates actively in interactions between epithelial and mesenchymal tissues, further knowledge of the pathogenesis of this tumour may be provided by the study of extracellular matrix components. Therefore, we have analysed the immunohistochemical distribution of type I, III, and IV collagen, fibronectin, laminin and tenascin in four cases of synovial sarcoma. The pattern of immunoreactivity for these molecules varied according to the tissue phenotype of the tumour. Mesenchymal tissue labelled mainly for type I and III interstitial collagen and fibronectin. The epithelial component was surrounded by a laminin and type IV collagen-positive basement membrane, but punctate pericellular reactivity for laminin and type IV collagen was also detected among some mesenchymal cells. Tenascin was strongly expressed in the mesenchymal tissue immediately around epithelial structures and weakly or not at all expressed in the monophasic tumours and in mesenchymal tissue distant from epithelial elements in the biphasic tumours. These results suggest some resemblances between synovial sarcoma and the embryonic development of epithelia from mesenchymal cells, providing further support for the concept of an epitheliogenesis from the mesenchyme in these tumours.