Polymorphous low-grade adenocarcinoma of minor salivary gland. A comparative histologic and immunohistochemical study.

Sixteen polymorphous low-grade adenocarcinomas were reviewed and compared with 17 adenoid cystic carcinomas and with 21 other histologically similar minor salivary gland neoplasms. The polymorphous low-grade adenocarcinomas were for the most part distinctive in their microscopic appearance. Typically they exhibited infiltrative growth by small uniform cells in single-layered ducts. A syncytium of tumor cells was also characteristic, although solid and cribriform patterns were seen, making definitive diagnosis difficult with some tumors. Immunohistochemical staining for S-100 protein, glial fibrillary acidic protein, actin, vimentin, and keratins resulted in relatively distinctive antigenic profiles for the tumors studied. Of significance was strong S-100 protein and weak actin staining of polymorphous low-grade adenocarcinomas, moderate actin staining of adenoid cystic carcinomas, moderate glial fibrillary acidic protein staining of monomorphic adenomas and pleomorphic adenomas, and nonreactivity of monomorphic adenomas for vimentin. It is believed that the immunoprofiles could be useful in the microscopic diagnosis of salivary gland tumors. The identification of antigens found normally in myoepithelial and epithelial cells supports the concept that these tumors are derived from pluripotential reserve cells.