Giant cell tumor of tendon sheath. An immunohistochemical observation on the characteristics and the capacity of proliferation of tumor cells.

To investigate character and proliferation of tumor cells of giant cell tumor of tendon sheath (GCTTS), we studied 25 cases of GCTTS by light and electron microscopic immunohistochemistry. Mononucleated stromal cells (SC) of GCTTS could be divided into three types according to their antigenic features. The first type was the histiocytic SC expressing antigens recognized by KP1, Mac387 and Ham56. The second type was the fibroblastic SC showing fibronectin immunoreactivity. The third type was the intermediate SC expressing both KP1 and fibronectin. The presence of intermediate SC suggested that the different types of SC of GCTTS would be of common origin, i.e. from the mesenchymal cells of the synovium and represented different functional phases or phenotypic alterations. The expression of proliferating cell nuclear antigen (PCNA) was observed only in SC and occasionally, in binucleated cells, but multinucleated giant cells (GC) were negative for PCNA, suggesting that GC were non-dividing cells.