Giant cell tumor of tendon sheath: immunohistochemical study of 20 cases.

AIMS AND BACKGROUND: Giant cell tumor of tendon sheath (GCTTS) is a common tumor occurring on the tendon sheaths of the fingers. The nature of this lesion is still controversial: some researchers consider it a reactive process arising from chronic inflammation while others regard it as a tumor of presumed synovial cell or monocytic macrophage system origin. In an effort to clarify the histogenesis we decided to further investigate the immunophenotypic profile of this tumor.

STUDY DESIGN: We studied 20 GCTTS of the fingers using a panel of 18 antibodies, 13 monoclonal and 5 polyclonal.

RESULTS: The immunohistochemical investigation revealed that the mononuclear cells of this lesion can be divided into two groups. The cells of the first and more numerous group were positive for vimentin, PG-M1 and KP1 but also for muscle actin (HHF35 monoclonal antibody) and neuron-specific enolase. A second population of mononuclear cells, usually arranged around the giant cells, were positive for PG-M1, KP1, LCA and occasionally for alpha-1-antitrypsin and alpha-1-antichymotrypsin. Multinucleated giant cells were also positive for KP1, PG-M1 and LCA monoclonal antibodies. A variable but usually weak positivity for alpha-1-antitrypsin, alpha-1-antichymotrypsin and lysozyme was also observed.

CONCLUSIONS: Our results suggest a synovial cell origin for GCTTS and do not support the hypothesis that it could be a neoplasm with a true histiocytic origin. The positivity of some cells for the HHF35 antibody, together with electron microscopic evidence of filament bundles with focal dense bodies, suggests that at least part of the mononuclear cells may have a myofibroblastic differentiation.