Answer: Adenosquamous carcinoma

Histology: The carcinoma is biphasic. The prominent component is that of an invasive partially keratinizing squamous cell carcinoma. It is closely associated with a minor component of a moderately differentiated adenocarcinoma with well formed glands. There is in-situ carcinoma of the excretory ducts with extension of dysplasia along the surface epithelium.

Discussion: Cases of adenosquamous carcinoma are unusual yet well documented in the head and neck. Most of these arise in the oral cavity or the larynx. We believe that the distinction of adenosquamous carcinoma from high grade mucoepidermoid carcinoma (MEC) is both microscopically feasible and clinically relevant. MEC usually presents with a more variable histologic picture (e.g. solid and cystic growth, more diverse cell types, etc…), demonstrates a more intimate admixture of the squamous and glandular components, and is not associated with dysplasia of the surface squamous epithelium. Clinically, adenosquamous carcinoma is more aggressive than MEC, even for those MECs that are high grade.

Sometimes the squamous cell carcinoma with pseudoglandular formations owing to tumor necrosis (i.e. acantholytic squamous cell carcinoma) may be mistaken for adenosquamous carcinoma. For acantholytic carcinoma, close inspection of the tumor will usually demonstrate degenerating tumor cells and nuclear debris within these spaces. If uncertainty persists, a mucicarmine stain for epithelial mucin should clarify the distinction between true and pseudoglandular formations.