tum or consisted of a firm , well - circumscribed , ovoid piece of soft pink tissue measuring 21.51 cm in the supraglottic area of the larynx . histologically , the mass showed a fibrous and chondromyxoid stroma containing epithelial and myoepithelial cells . epithelial component consisted of relatively uniform - appearing cells arranged in tubules and small , nested aggregates ( figure 1 ) myoepithelial component was positive for p63 , s100 protein ( figure 2a ) , and glial fibrillary acidic protein ( gfap ) ( figure 2b ) ; and focally positive smooth muscle actin ( sma ) . ( a - b ) hematoxylin and eosin ( h&e ) stained section showing sheets of myoepithelial cells and ductular structures lined with epithelial cells set in chondromyxoid stroma ( h&e , a : 40 ; b : 100 ) . ( c ) adjacent to the lesion , normal laryngeal cartilage can be seen ( h&e , 100 ) . immunohistochemistry indicates that the myoepithelial cells cytoplasm is focally positive for s100 protein ( a ) and glial fibrillary acidic protein ( gfap ) ( b ) ( a : 100 ; b : 100 ) . pa is a commonly diagnosed benign tumor in the salivary glands that may also occur in a variety of other sites ; however , it is rarely seen in the larynx . the diagnosis of pa is simple , but when it grows in an unusual site like the larynx , it can be mistaken for a malignant neoplasm . pleomorphic adenomas are characterized by epithelial tissue mixed with tissues of myxoid , mucoid or chondroid appearance . histologically , pleomorphic adenoma of the larynx may resemble aggressive epithelial tumors because of the high cellularity and lack of a stromal component . importantly , this feature is not in keeping with that of major salivary glands , which demonstrate relatively reduced myoepithelial cellularity . occasionally , pleomorphic adenomas are composed almost entirely of epithelial cells with few or no stromata myoepithelial cells are variably positive for s100 protein , sma , gfap , calponin , and cd10 . although pa is a benign tumor , it can cause problems in clinical management due to its tendency to recur and risk of malignant transformation . histological features indicative of malignant transformation include cytological atypia , increased mitotic figures , satellite tumor nodules , tumor necrosis , and infiltrative margins7 . pas have tendency to recur when not widely excised , particularly if they are predominantly mucoid , and have variability in the thickness of the capsule and the tumor invading the capsule . in addition , due to low biological requirements , the neoplastic cells can survive when spilt into the operative sites . pas should be differentially diagnosed from other tumors such as carcinoma ex pleomorphic adenoma , adenoid cystic carcinoma , basal cell carcinoma , basal cell adenoma , myoepithelioma , polymorphous low - grade adenocarcinoma , angiofibroma , hamartoma , epidermoid cyst , hemangioma , vascular malformations , nasopharyngeal carcinoma , and nonepithelial tumors . carcinoma ex pleomorphic adenoma exhibits extensively infiltrative malignancy with necrosis , perineurial invasion , frequent mitotic figures , marked nuclear atypia . adenoid cystic carcinoma usually shows cribriform , solid or tubular pattern similar to cylindromas of the skin . it is composed of small , bland myoepithelial cells with scant cytoplasm and dark , compact , angular nuclei that surround pseudoglandular spaces with periodic - acid schiff ( pas)-positive excess basement membrane material and mucin . peripheral perineurial invasion and small , true , glandular lumina are sometimes seen , but no squamous differentiation , and extensive necrosis is usually absent . adenoid cystic carcinoma has high proliferative index , high p53 immunoreactivity , and intense staining for b - cell lymphoma 2 ( bcl 2 ) , but negative reactivity for glial fibrillary acidic protein . in contrast , pleomorphic adenoma is not invasive , shows no perineurial invasion and has squamous metaplasia and mesenchyme - like areas . it is an infiltrative tumor with perineurial invasion and vascular invasion as well as variable cytologic atypia and mitotic activity . it is composed of solid , trabecular , tubular or membranous patterns , but no myxoid matrix or cartilagenous areas . basal cell adenoma is composed of basaloid cells sharply delineated from the stroma by basement membrane . polymorphous low - grade adenocarcinoma is usually a nonencapsulated tumor with diverse ( polymorphous ) growth patterns , infiltrative borders , perineurial invasion and tumor necrosis is rare . differential diagnosis of pa consists of myoepithelioma , a benign epithelial salivary gland tumor , and presence of plasmacytoid or spindled myoepithelial cells . additionally , basal cell adenoma may also be involved in the differential diagnosis . to conclude , pleomorphic adenoma of the larynx is a rare neoplasm and therefore its diagnosis requires a high index of suspicion . recurrence many years after surgical excision as well as malignant transformation should be a concern and therefore long - term follow - up is necessary .