Polymorphous low-grade adenocarcinoma of minor salivary gland. An immunohistochemical and clinicopathologic study.

Polymorphous low-grade adenocarcinoma (PLGA) is a minor salivary gland carcinoma usually arising intraorally, primarily in the palate. It is characterized by cytologic uniformity, histologic blandness, and a variable, infiltrating growth pattern. To date, 117 tumors have been reported but the immunohistochemical features of this neoplasm have not been adequately described. This report describes the immunohistochemical distribution of epithelial membrane antigen (EMA), carcinoembryonic antigen (CEA), high-molecular-weight keratin, muscle-specific actin (MSA), and S-100 protein in four palatal polymorphous low-grade adenocarcinomas arising in two men and two women. Three patients were treated with a combination of radiation and surgery, and one was treated with just surgery; none of the tumors recurred or metastasized. More than 90% of tumor cells in all four tumors stained with S-100 and EMA, while 75 to 95% stained with keratin. MSA staining intensity was variable; it ranged from less than 10% to 67% of tumor cells staining positively. CEA staining also was markedly variable; it ranged from very focal luminal positivity to 75% of tumor cells staining positive. The diffuse staining pattern of EMA and S-100 and the difference in staining patterns of EMA and CEA in PLGA is distinct from that found in adenoid cystic carcinoma. In the latter neoplasm, EMA and CEA staining patterns are similar and they are localized to ductal lumina; S-100 stains much less diffusely. These differences are useful in the differential diagnosis between these two tumors.