Palisading adenocarcinoma. State of the art and first case report in the parotid gland of a 44-year-old woman

Palisading adenocarcinoma is a newly described salivary gland tumor known for its predilection for sublingual and submandibular glands. The mass tends to have a non-invasive growth, although signs of infiltrative growth can occur resulting in a neoformation more adherent to deep neck structures. The main histological feature is a biphasic cellular pattern composed of polygonal epithelioid cells with small nuclei arranged in trabeculae and pseudo-rosette like structures and a second population of scattered well-formed ductal structures with occasional mucocytes. The mass, located in the parotid gland, resembled a neuroendocrine neoplasia regarding its histological architecture and positivity for CD56, whereas the cytological examination resembled that of a pleomorphic adenoma. An accurate histological and immunohistochemical study was crucial to guide the differential diagnosis. Here we present the first case of palisading adenocarcinoma affecting the parotid gland to further enrich the literature and to shed additional light on this peculiar and recently investigated neoplastic entity.