Polymorphous Low-Grade Adenocarcinoma

Polymorphous low-grade adenocarcinomas are minor salivary gland neoplasms with a predilection for intraoral sites. Women are affected twice as frequently as men, and generally present in the fifth to sixth decade of life with a painless intraoral mass. The palatal mass is, on average, about 2 cm in greatest dimension. The tumors are submucosal, identified below an intact mucosa as a well-circumscribed although unencapsulated mass. The tumor is characterized by a polymorphous growth pattern, with individual tumors demonstrating multiple patterns, including solid, ductal–tubular, cribriform, trabecular, and single-file growth. Neurotropism is common, frequently forming a central nidus around which a “targetoid” pattern is formed. The neoplastic cells are isomorphic, containing round to oval vesicular nuclei with small nucleoli. Mitotic activity and necrosis are inconspicuous. There is frequently a slate gray-blue stroma separating the tumor cells. Immunohistochemical analysis demonstrates reactivity with cytokeratin, vimentin, S-100 protein, CD117, glial fibrillary acidic protein, and actin. Bcl-2 is overexpressed and there is generally a low proliferation index as determined by Ki-67 reactions. The tumor must be separated from pleomorphic adenoma (benign mixed tumor) and adenoid cystic carcinoma. Complete surgical excision will yield a more than 95% 10-year survival, although persistence or recurrence can emerge often in about 10% of patients more than 10 years later.