Myoepithelioma-New Concepts of Histology and Classification: A Light and Electron Microscopic Study

Abstract

Based on histological, immunohistochemical, and ultrastructural studies, it is now apparent that the modified myoepithelial cell component of pleomorphic adenomas has a considerable range of cytological features. We reasoned that myoepitheliomas could be tumors with a similar spectrum of neoplastic myoepithelium but lacking the ductal element displayed in pleomorphic adenomas. A review of available salivary gland tumors identified 40 examples based on this definition. Architecturally, these myoepitheliomas displayed either nonmyxoid (solid), myxoid (pleomorphic adenoma-like), reticular (canalicularlike), or mixed growth patterns, while cytologically the lesions were composed of spindle-type (32.5%), hyaline-type (7.5%), epithelial-type (45.0%), clear-type (2.5%), or mixed-type (12.5%) tumor cells. Electron microscopy was carried out on eight examples and detailed immunohistochemistry on two methanol-fixed cases. As a result of the current review of myoepitheliomas and the description of similar lesions in the literature, it is our contention that salivary gland myoepitheliomas are not as rare as has been purported.

Cytohistological Study of Salivary Gland Lesions

“…Few areas showed hyalinisation. Similar observations were made by studies done by Simpson et al 15 and Dardick I et al 16 In the present study one case of basal cell adenoma [ Figure 4] was seen constituting to 1.92% of all tumours. Grossly the tumour showed irregular, grey white nodular mass.…”

Secretory Myoepithelial Carcinoma: A Histologic and Molecular Survey and a Proposed Nomenclature for Mucin Producing Signet Ring Tumors

“…Neoplastic or 'modified' myoepithelial cells may not express all myoepithelial markers, and may lose some ultrastructural hallmarks that are expected in normal myoepithelial cells though immune-electron microscopy may still show muscle marker expression [15,16]. In fact, Dardick et al [17] even describe a metastasis from a myoepithelial carcinoma showing early acinar differentiation by electron microscopy, suggesting that neoplastic myoepithelial cells may not only have incomplete myoepithelial characteristics, but in some cases may show transdifferentiation towards a luminal phenotype.…”

Myoepithelioma of Tongue

“…The traditional definition included only three types of myoepithelioma: plasmacytoid, spindle and mixed cells forms [4,8]. However, with the recent recognition of the different phenotypic and ultrastructural modifications displayed by the neoplastic myoepithelial cells of salivary gland tumours, the morphologic spectrum of myoepithelioma has been expanded [10,14]. By taking into account the variety of cytoarchitectural patterns displayed by the myoepitheliomatous regions of pleomorphic adenoma, Dardick et al have proposed broader histopathologic guidelines for myoepitheliomas and have included a few previously unrecognized variants [14,15] .…”