Aggressive oral carcinoma cuniculatum: A rare entity.

Oral carcinoma cuniculatum (OCC) is a rare and distinct clinicopathological variant of oral squamous cell carcinoma (OSCC). The term cuniculatum was derived from a Latin word "cuniculus" meaning burrow, because of the "rabbit burrow" appearance. As it invades the underlying tissue, it forms crypts filled with keratin that are essential in distinguishing this neoplasm from other variants of squamous cell carcinoma (SCC). It is a common lesion of the plantar region of the foot but rare in the oral cavity. The first case of OCC was reported in 1977 by Flieger and Owenski in the jaw, with fewer than 50 cases reported in the English literature till date. Tumor cell cannibalism has been reported in various carcinomas such as lung, gallbladder, hepatobiliary, pancreatic, and SCC. Cell cannibalism when it refers to a cancer cell, either within a tumor mass or cell culture, is "a cell that is contained within another bigger cell with a crescent-shaped nucleus." This report aims to present a rare case of aggressive OCC of the maxillary gingiva with cellular cannibalism and its diverse immunohistochemical expression of E-cadherin, Ki-67, and p53.