Definition : It is benign tumor having epithelial origin with cells demonstrating both mesenchymal and epithelial differentiation.
It is termed as pleomorphic adenoma as tumor exhibits morphologic diversity.
Also termed as Mixed tumor as it has both epithelial and mesenchymal like elements.
Incidence : constitutes 74% of salivary gland tumors and 66% of the benign salivary gland tumors
Site : Common site – parotid gland. other common sites are submandibular glands, palate, upper lip and buccal mucosa
Age and sex: Can occur in any age with slight female predominance
Clinical features : presents as slow growing painless nodular firm mass located below and infront of the ear
Morphology
Gross :
Well encapsulated, round to ovoid mass with smooth nodular surface
Cut surface is gray white with translucent zones representing cartilaginous and myxochondroid areas
Microscopic findings
Capsulated lesion composed of epithelial and mesenchymal like tissues
Epithelial component consists of well formed ducts, sheets, cords, anastomosing trabeculae and cystic spaces. Epithelial cell types are cuboidal, basaloid, plasmacytoid, spindle shaped, oncocytic or squamous.
Mesenchymal like component is constituted by myxoid, hyaline, chondroid and osseous areas.
PAS positive material is seen in the lumen of the cystic spaces
Immunohistochemistry
S-100 positivity in epithelial and stromal regions
Myoepithelial cells show positivity with smooth muscle specific protein, Calponin and cytokeratin (CK 19)
Treatment and prognosis
Complete surgical resection is the treatment of choice.
Recurrences can occur due to the failure of removal of the tumor tissue which protrudes from the capsule into the adjacent tissue.
Malignant transformation can occur (Carcinoma ex pleomorphic adenoma)
