PCNA and Ki-67 immunoreactivity in multinucleated cells of giant cell fibroma and peripheral giant cell granuloma.

Immunohistochemical investigation of PCNA and Ki-67, two diverse nuclear proteins essential to the cell cycle, was undertaken in archival, formalin-fixed and paraffin-embedded specimens of giant cell fibroma (GCF) and peripheral giant cell granuloma (PGCG++). GCF multinucleated cell nuclei were mostly PCNA+, although there was variability in staining intensity. This indicates heterogeneity in nuclear PCNA metabolism of GCF multinucleated cells, and it is possible that the most intensely stained nuclei have passed through the cell cycle more recently compared to the less immunoreactive nuclei. However, the absence of Ki-67 immunoreactivity in GCF multinucleated cells, and absence of mitoses in GCF multinucleated cells, suggests that cell cycling in the absence of cytokinesis is not involved in GCF multinucleated cell formation. Alternatively, GCF multinucleated cells possibly form by fusion of mononuclear cells previously identified as fibroblasts, although this theory cannot be confirmed by the data presented in this study, and the histogenesis of GCF multinucleated cells remains unclear. In contrast, absence of either PCNA or Ki-67 immunoreactivity in PGCG multinucleated cells is consistent with an osteoclast lineage and formation from differentiated mononuclear cells.