RESUMEN
BACKGROUND: Ossifying fibromyxoid tumors (OFTs) are uncommon soft tissue neoplasms. Only one case arising in the gingiva has been described. METHODS: A 21-year-old woman presented with a painless exophytic mass located in the right posterior mandibular gingiva, which was identified 6 months earlier. Radiographs showed irregular calcifications inside the lesion, discrete irregularity of alveolar bone, and integrity of buccal and lingual cortical bone. An incisional biopsy was performed based on the clinical diagnostic hypothesis of peripheral ossifying fibroma or peripheral giant cell granuloma. Microscopic features were compatible with the diagnosis of ossifying fibroma. The entire mass was excised and submitted to histopathologic and immunohistochemical analysis. RESULTS: Histopathologic analysis revealed proliferation of round to spindle-shaped cells arranged in cords and nests and embedded in a fibromyxoid matrix. An incomplete shell of bone trabeculae located beneath the fibrous pseudocapsule was observed at the periphery. Immunohistochemical analysis showed positivity for vimentin and S-100 protein and negativity for smooth muscle actin, muscle-specific actin, and glial fibrillary acidic protein. The definitive diagnosis was OFT. The patient showed no clinical signs of recurrence 7 months after surgical excision. CONCLUSIONS: OFTs located in the gingiva are extremely rare. At this site, these tumors are clinically indistinguishable from other reactive or neoplastic lesions. Although many cases present an indolent biologic behavior, the local recurrence of OFTs has been reported; therefore, long-term follow-up is mandatory.