Metastasizing pleomorphic adenoma of the parotid gland

Salivary gland tumours are estimated to represent approximately 3% of all head and neck tumours. About 70-80% of these neoplasms occur in the major salivary glands, with the parotid gland being the most commonly affected site. The metastasizing pleomorphic adenoma (MPA) has histological characteristics of pleomorphic adenoma, but it has the capacity to generate local recurrences and distant metastases (mainly bones, lungs, and lymph nodes). Despite the fact that some authors consider it to be a benign neoplasia, the 2015 World Health Organisation (WHO) classification of head and neck tumours considers it to be malignant. We present a highly unusual case of metastasizing pleomorphic adenoma of the parotid gland and a bibliographic review.