Carcinoma cuniculatum (CC) is a rare variant of low-grade squamous cell carcinoma (SCC), and occurrence in the oral cavity is quite unusual. CC has a papillomatous keratinized surface like verrucous carcinoma, but CC has a propensity for aggressive local invasion, especially into the bone. Therefore, CC can be quite difficult to remove surgically. A 68-year-old man presented with a case of CC mimicking verrucous leukoplakia in the mandibular gingiva. Repeated biopsies showed no malignancy. Local resection was performed, and histological examination revealed the presence of well-differentiated SCC. Additional hemi-mandibulectomy was performed and the final histological diagnosis was CC. Local recurrence was detected at the 14-month follow-up examination. Chemotherapy with docetaxel was not effective, and he died of aspiration pneumonia. CC of the oral cavity is a rare entity and the diagnosis is hard to establish. Misdiagnosis could result in inadequate removal and local recurrence. Complete resection with a safety margin is essential because of the tendency for local invasion.
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