Carcinoma cuniculatum of the jaw: a rare variant of oral carcinoma.

Carcinoma cuniculatum is a rare variant of carcinoma usually involving the foot. Only 13 cases have been described in the oral cavity, none of which was in the English-language literature. We describe a 56-year-old man who presented with a soft exophytic mass in the maxillary gingiva, alveolar bone destruction, and loosening of the teeth. Histopathologic study revealed thin papillary projections covered by a thick keratin layer in the superficial areas and multiple, branching keratin-filled crypts surrounded by well-differentiated squamous epithelium with only mild cytologic atypia but frequent mitosis. Immunohistochemistry results of p53 and polymerase chain reaction analyses for human papillomavirus 6, 11, 16, and 18 DNA were negative. The diagnosis was carcinoma cuniculatum of the jaw. The literature on this unusual oral pathosis is reviewed and the diagnostic challenge described. We suggest that carcinoma cuniculatum may sometimes be misdiagnosed as squamous cell carcinoma or verrucous carcinoma and, therefore, might be more prevalent than the small number of published cases implies.