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Giant cell tumor of bone is a locally aggressive bone tumor characterized by the proliferation of round-to-oval mononuclear cells and uniformly distributed osteoclast-type giant cells. Giant cell tumor of bone typically arises in long bones, whereas craniofacial involvement is rare. Atypical histological and clinical presentations can complicate diagnosis. This study presents a challenging case of giant cell tumor of bone in the mandible.

A Japanese man in his 70s presented with a slowly expanding radiolucent lesion in the left mandible, first noted a decade ago, with no subjective symptoms. Cone-beam computed tomography revealed a 27 mm × 12 mm × 23 mm radiolucent lesion with irregular borders and discontinuity of the mandibular canal. Excisional biopsy showed the proliferation of bland spindle cells with small multinucleated cells, which indicated central giant cell granuloma. However, the spindle cells were positive for H3.3G34W, a specific marker of giant cell tumor of bone, which confirmed the diagnosis of giant cell tumor of bone. Conventional histological features of giant cell tumor of bone were absent throughout the observation period.

Morphological analysis alone is insufficient for diagnosing giant cell tumor of bone, and H3.3G34W immunostaining is valuable in distinguishing it from other giant cell lesions. The possibility of giant cell tumor of bone should not be ruled out in cases involving the jaw, although its occurrence is rare.