Metatypical Adenoid Cystic Carcinoma of the Palate

The term "metatypical" is anecdotally employed to describe histopathological variations that can be found in salivary gland adenoid cystic carcinoma.

A 68-year-old man presented with a painful palatal nodule developed over the period of 6 months. A cone beam computed tomography showed a soft tissue-based mass with penetration into maxillary bone. An incisional biopsy was performed.

The histopathology revealed a biphasic tumor predominantly composed by myoepithelial-type basaloid cells arranged in trabeculae and macrocysts with focal squamous differentiation. Occasional intervening ducts were observed. Immunohistochemical reactions highlighted the myoepithelial nature of basaloid cells, which were positive to cytokeratin 14 and smooth muscle actin, whereas the duct-forming cells were positive to cytokeratin 7 and cytokeratin 14. A small focus of conventional cribriform adenoid cystic carcinoma was identified at the periphery of the specimen. The diagnosis of metatypical adenoid cystic carcinoma was established CONCLUSIONS: The morphological diversity of metatypical adenoid cystic carcinoma represents a potential diagnostic pitfall in surgical pathology practice, particularly if the metatypical components are predominant and overlap the conventional areas. The list of differential diagnoses to be considered includes benign and malignant salivary and odontogenic tumors, but the adequate tumor classification is fundamental to ensure an appropriate treatment strategy for a long-term disease control.