We report a case of polymorphous low-grade adenocarcinoma (PLGA) involving the hard palate of a 71-year-old woman.Physical examination revealed a 19×17mm painless swelling of the palate without mucosal ulceration. The cervical lymphnodes were not palpabe. Clinical diagnosis of minor salivary gland tumor was made, and an excisional biopsy was performed. She recovered uneventfully, and no additional therapy was administered. She has remained disease-free for 30 months after the operation.
The excised specimen consisted of a circumscribed but unencapsulated, grey/white-to-tan mass with an intact overlying mucosa. Microscopically, the tumor contained a variety of growth patterns: solid, trabecular, cribriform, papillary, and monolayered tubular structures. The tumor cells were uniform with bland oval nuclei, and mitotic figures were not seen.The resection margins were not involved. Immunohistochemically, most of the tumor cells showed positive staining for vimentin, S-100 protein, and sometimes for muscle-specific actin, as well as for cytokeratin, indicative of their neoplastic myoepithelial natures. It is interesting that some of these were also positive for epithelial membrane antigen. On the other hand, the tumor cells were entirely negative for glial fibrillary acidic protein. These immunoprofiles may be useful in distinguishing PLGA from other salivary gland tumors bearing histologic resemblances.
