Primary unilateral multifocal pleomorphic adenoma of the parotid gland: molecular assessment and literature review.

Multiple separate tumors developing in a single salivary gland is rare in previously untreated patients. Tumors that can be multicentric include Warthin tumor, oncocytoma, basal cell adenoma and acinic cell carcinoma. The incidence of multiple primary unilateral pleomorphic adenomas is extremely rare in patients with no prior history of trauma or surgery. We report two cases of primary multicentric pleomorphic adenoma and review the literature. We also subjected one of our cases to a molecular clonality test. The molecular results suggested that the separate nodules were clonally related, arguing against an independent origin.