Polymorphous low grade adenocarcinoma of minor salivary gland: a clinicopathologic and comparative immunohistochemical study.

Retrospective review of seven cases of polymorphous low grade adenocarcinoma (PLGA) revealed that the original histologic diagnosis in five instances was mixed tumor (four benign and one malignant). Comparison of PLGA tumors with eleven representative cases of benign pleomorphic adenoma of minor salivary gland (BPA) showed marked similarity in cytologic features. PLGA and BPA also exhibited similar mucohyaline and/or fibromyxoid stromal components. In contrast, tumor margins of the two neoplasms were quite different; margins of PLGA were consistently infiltrative, whereas those of BPA were generally well circumscribed and encapsulated. Immunophenotypic comparison confirmed the glial fibrillary acidic protein (GFAP) positivity in BPA reported by others, whereas cases of PLGA were uniformly nonreactive with this antibody. Although previous reports have emphasized the histologic similarities of PLGA and adenoid cystic carcinoma, our findings indicate that differentiation of PLGA from BPA may represent a more common diagnostic problem. Awareness of comparative histologic features is important in the differential diagnosis of these minor salivary gland neoplasms. Also, monoclonal GFAP may be useful in distinguishing cases of PLGA from BPA where histologic features are otherwise similar.