A case of giant cell tumor of the tendon sheath developing on the palm

A 22-year-old Japanese woman with a giant cell tumor of the tendon sheath on the palm is described. The location of the tumor is rare. Light microscopically, the tumor consisted of round or polygonal cells, giant cells, and foam cells. Electron microscopically, histiocyte-like cells and fibroblast-like cells were mainly observed, suggesting that the tumor may have originated from the synovial membrane.