Answer: Squamous cell carcinoma, papillary variant

Histology: At low power, the tumor demonstrates an exophytic pattern of growth characterized by numerous surface papillations. The papillary fronds are lined by a thickened and dyspolarized layer of atypical cells. The atypical cells have a immature basal cell-like appearance. Mitotic figures are abundant. Owing to the exophytic nature of the lesion, the biopsy fragments are relatively superficial and do not include the base of the lesion at its interface with the underlying stroma.

Discussion: Papillary squamous cell carcinoma represents one of several variants of conventional squamous cell carcinoma of the head and neck. This particular variant is characterized by the presence of well formed complex papillae. Although its papillary growth pattern may cause confusion with squamous papilloma or a Schneiderian papilloma, an appreciation for the pleomorphism and brisk mitotic activity of the cells lining the papillae should dispel any uncertainty.

Although the papillary component is considered to be a form of in-situ (i.e. non-invasive) carcinoma, it is often associated with an invasive component in the deeper portions of the lesion. This invasive component typically takes on the appearance of conventional infiltrating squamous carcinoma. Because of its prominent exophytic growth, the base of the lesion is often inadequately sampled by the surgeon, rendering the distinction between non-invasive and invasive forms of papillary squamous cell carcinoma difficult if not impossible during endoscopic biopsy. Once the exophytic component of the lesion, the surgeon should be encouraged to obtain additional biopsies from the base of the lesion so that it can be assessed for invasive growth.