Relationship between binuclear and multinuclear cells in giant cell tumor of bone

Giant cell tumor of bone (GCT) consists of stromal and multinuclear type tumor cells. Although most people believe that the stromal cells are mononuclear, we recently found the existence of many binuclear cells among stromal cells using DNA cytofluorometric examination. This study, using 18 tumors of GCT was conducted to elucidate the cell biological significance of the binuclear cell, especially its relationship to multinuclear cell formation or tumor cell proliferation. The investigation was carried out by means of DNA-RNA cytofluorometry with acridine orange (AO) and histological method. Using fluorescence microscopic observation, we counted the numbers of both mononuclear and binuclear cells and calculated the index of % BNC, which expresses the frequency (percentage) of binuclear cells in a population of mononuclear and binuclear cells. The index of % S-G2 obtained by DNA-RNA cytofluorometry showed the frequency (percentage) of mononuclear cells in the S and G2 phases of the cell cycle. In the histological study, we counted the numbers of multinuclear giant cells with more than 3 nuclei in the cytoplasm and stromal cells including mononuclear and binuclear cells and calculated MNS/SC, which showed the percentage of multinuclear cells in the stromal cells in the microscopic field. Eight tumors showed a value of % BNC greater than 10% and 2 had a value of 40%. The index of % BNC significantly correlated with the average value of MNC/SC in all tumors. There was no significant correlation between % BNC and the average value of % S-G2, in 18 tumors although 4 tumors having a % BNC value greater than 20% showed a % S-G2 value greater than 12% in 18 tumors. These results revealed the presence of many binuclear cells among stromal cells of GCT and suggested that these binuclear cells might be formed in association with the active proliferation of mononuclear cells and closely relate to the formation of multinuclear giant cells.