Polymorphous low-grade adenocarcinoma: a case report with ultrastructural findings.

A specimen of a polymorphous low-grade adenocarcinoma of minor salivary gland origin in the nose, originally diagnosed as an adenoid cystic carcinoma, was examined by electron microscopy. The tumor cells forming narrow, anastomosing trabecular cords in histologic sections were almost exclusively well-differentiated myoepithelial cells when examined with the electron microscope. Adenoidal regions within and between the columns of tumor cells resulted from the production of excessive amounts of basal lamina and glycosaminoglycans. In one focal region, glandular lumina were formed within the trabecular cords and more solid regions of the tumor. By both immunohistochemistry (anticytokeratins and anti-S 100 protein) and electron microscopy, transitions from the principal tumor cells comprising the trabecular cords (myoepithelial cells) to luminal epithelial cells could be detected. Since the patient is free of recurrence or metastases 7 years after limited surgical resection of the tumor, the designation of polymorphous low-grade adenocarcinoma seems quite appropriate.