Giant cell tumor bone. Enzyme histochemical, biochemical and tissue culture studies.

Three giant cell tumors of bone (2 benign and 1 malignant) were examined enzyme-histochemically, and a tissue culture study of the malignant case was performed. Multinucleated giant cells and mononuclear round cells had similar activities of ACPase and non-specific esterase with a diffuse strong reaction. ATPase and 5'-nucleotidase reactions were strongly positive in the cytoplasm of multinucleated giant cells, and were seen not only in the cytoplasm but also on the cell membrane of round cells. The proliferating spindle cells in the malignant case were faintly positive for ACPase and non-specific esterase and were less positive for ATPase and 5'-nucleotidase on the cell membrane. The multinucleated giant cells and mononuclear round cells resembled histiocytes in the activities of 4 hydrolytic enzymes, and the multinucleated giant cells had enzyme activities similar to those of osteoclasts from new-born rat skull. The malignant giant cell tumor and cells in its tissue culture showed ALPase activity preferentially on the cell membrane of the spindle cells, and rarely on round cells or multinucleated giant cells. ALPase was resistant to heat treatment and was found to be the type IV isoenzyme by diffusion electrophoresis. The origin of the giant cell tumor of bone and the significance of the ALPase activity are discussed.