Basal cell carcinoma of the buccal mucosa.

True basal cell carcinoma (BCC) involving the oral mucous membranes is extraordinarily rare. Most of those described as occurring in the oral cavity usually involve the gingiva and are not true BCCs but peripheral ameloblastomas. A true BCC, which arose on the buccal mucosa of a 69-year old man, is reported. It presented as a 1.3 cm ulcerated plaque without gingival connection. Histologically, the lesion exhibited classic features of BCC with palisading and retraction spaces, and focally communicated with the overlying squamous epithelium. Although it is possible that this lesion also arose from a heterotopic odontogenic rest, the anatomical location, focal squamous (metatypical) features, and positive staining for Ber-EP4 support an origin from the basal cell layer of stratified squamous mucosa.