The myoepithelial immunophenotype in 135 benign and malignant salivary gland tumors other than pleomorphic adenoma

Background. We have previously studied the immunoreactivity of 3 novel smooth muscle-specific proteins, α-smooth muscle actin, smooth muscle myosin heavy chains, and calponin, to assess myoepithelial differentiation in pleomorphic adenomas. Objective. To further expand our knowledge of myoepithelial differentiation in other benign and malignant salivary gland tumors. Design. Formalin-fixed paraffin sections of 135 salivary gland tumors with associated normal glands were stained with monoclonal antibodies using the avidin-biotin complex immunoperoxidase method and enzymatic and microwave heat-induced epitope retrieval. Results. In adenoid cystic carcinomas and epithelialmyoepithelial carcinomas, all 3 markers exclusively highlighted the myoepithelial cell components and the epithelial cells were entirely negative. No immunostaining was detected in canalicular adenomas, oncocytomas, Warthin tumors, acinic cell carcinomas, mucoepidermoid carcinomas, squamous cell carcinomas, and polymorphous lowgrade adenocarcinomas. Salivary duct carcinomas and adenocarcinomas, not otherwise specified had a distinctive pattern of uniform periductal staining of reactive myofibroblastic cells, and in salivary duct carcinomas some ducts retained a peripheral immunoreactive myoepithelial cell layer. Conclusion. Immunoreactivity for these 3 smooth muscle-specific proteins confirms the known neoplastic myoepithelial component of adenoid cystic carcinomas and epithelial-myoepithelial carcinomas. The consistently positive staining pattern in adenoid cystic carcinomas may be diagnostically useful in discriminating histologically similar but consistently negative polymorphous low-grade adenocarcinomas. Periductal linear staining in adenocarcinoma, not otherwise specified and salivary duct carcinomas is distinctive and appears to represent a tight cuff of myofibroblasts associated with the infiltrating glands.