Monoclonal origin of primary unilateral multifocal pleomorphic adenoma of the parotid gland.

Primary multiple pleomorphic adenomas in a unilateral parotid gland in previously untreated patients is a rare finding, and little is known about the etiology and pathogenesis. Here, a highly unusual case of a primary multifocal pleomorphic adenoma consisting of 15 individual nodules is presented. It is shown that all nodes are clonally related and thus share a common cell of origin excluding an independent multifocal pathogenesis. Most likely, multifocal pleomorphic adenoma represents parasitic nodules that have been detached from a main nodule, which may have been the result of undisclosed trauma.