Carcinoma Cuniculatum of the Oral Cavity: A Series of 6 Cases and Review of Literature.

Carcinoma cuniculatum (CC) is a rare variant of squamous cell carcinoma (SCC) that is characterized by minimal cytologic atypia and a unique deeply infiltrative growth pattern resembling rabbit burrows (cuniculi). With less than 75 cases reported in the head and neck, the clinical and pathologic spectrum of this entity remains poorly understood. A retrospective review of the clinical and pathologic features of archival cases of oral CC was performed. A total of six cases of oral CC were identified. Age ranged from 25-77 years; the male-to-female ratio was 5:1. All patients had a long-standing history of tobacco and betel-quid consumption. The tumors were distributed in the gingivobuccal sulcus (n = 2), the tongue (n = 2), buccal mucosa (n = 1), and the palate (n = 1). Histology in all cases typically revealed a tumor composed of well-differentiated squamous epithelium, devoid of atypia, lining deeply infiltrative, large-sized, branching, keratin-filled cavities, resembling rabbit-burrows. Dense lymphocytic infiltrates and discharging micro-abscesses were regular features. Underlying bone invasion and lymph node metastasis were observed in 1 patient. One patient with a tongue tumor developed locoregional recurrence at 10 months while none developed distant metastasis. Oral CC is a rare and under-recognized variant of SCC with locally aggressive behavior. Lack of familiarity with this variant exacerbated by the absence of cytologic anaplasia makes CC susceptible to multiple negative biopsies and erroneous diagnoses. Awareness of this clinicopathologic entity is essential to allow its accurate diagnosis and optimal management.