Osteoclastic-like giant cell tumour in a cat.

An 11-year-old neutered male domestic shorthair cat was presented with an epulis. A hemispherical mass, 8mm in maximum diameter, without a peduncle and bright reddish in colour, was observed on the gingiva of the left mandible. Radiography failed to show any infiltrating osteolysis. The epulis was surgically removed via gingival incision around the margin to the depth of connective tissue layer. Histopathological examination indicated that the epulis contained a large number of multinucleated giant cells (MGCs) intermixed with mononuclear mesenchymal cells in a loose fibrovascular stroma. Mitotic cells were found, mainly in the centre of the mass. MGCs were stained positive by the tartrase resistant acid phosphatase (TRAP) staining, indicating osteoclasts activity. Immunohistochemical staining for proliferating-cell nuclear antigen (PCNA) was observed within the majority of mononucleated cells, whereas multinucleated cells did not stain. An osteoclast-like giant cell tumour was concluded in this case. The origin of epulis is likely from the periosteal tissue. The cat recovered uneventfully and no recurrence has been noted for 3 years thereafter.