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 smoo th muscle-specific proteins, alpha-smooth muscle actin, smooth muscle myosi n heavy chains, and calponin, to assess myoepithelial differentiation in pl eomorphic 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 h eat-induced epitope retrieval. Results.-In adenoid cystic carcinomas and epithelial-myoepithelial carcinom as, all 3 markers exclusively highlighted the myoepithelial cell components and the epithelial cells were entirely negative. No immunostaining was det ected in canalicular adenomas, oncocytomas, Warthin tumors, acinic cell car cinomas, mucoepidermoid carcino-mas, squamous cell carcinomas, and polymorp hous lowgrade adenocarcinomas. Salivary duct carcinomas and adenocarcinomas , not otherwise specified had a distinctive pattern of uniform periductal s taining 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 co nfirms the known neoplastic myoepithelial component of adenoid cystic carci nomas and epithelial-myoepithelial carcinomas. The consistently positive st aining pattern in adenoid cystic carcinomas may be diagnostically useful in discriminating histologically similar but consistently negative polymorpho us low-grade adenocarcinomas. Periductal linear staining in adenocarcinoma, not otherwise specified and salivary duct carcinomas is distinctive and ap pears to represent a tight cuff of myofibroblasts associated with the infil trating glands.