Metastatic pleomorphic adenoma (MPA) is a histologically benign but clinically malignant unusual and potentially lethal manifestation of pleomorphic adenoma (PA). Patients at risk of MPA have a history of recurrent or incompletely treated PA, and as no current molecular or histological parameters can predict the development of MPA, such patients should be considered for screening for metastatic disease.

From the manuscript

Metastatic pleomorphic adenoma to the supraspinatus muscle: a case report and review of a rare aggressive clinical entity

Abstract
We report a case of a 65-year-old female with a recurrent right parotid pleomorphic adenoma (PA) 24 years after initial surgical excision. Positron-emission tomography (PET) and computed tomography (CT) demonstrated an unusual suspicious FDG-avid erosive rim enhancing mass centered in the right supraspinatus muscle. Cytology from CT-guided aspiration of the mass was consistent with a histologically benign PA, and the patient was diagnosed with metastatic pleomorphic adenoma (MPA). The patient later developed diffuse pulmonary metastases and died within 3 months. MPA, although rare, is recognised as a potentially lethal malignant complication of recurrent or longstanding benign PA. As no biochemical or genetic parameters are predictive of malignant change, patients presenting with recurrent PA should be considered for screening for metastatic disease.