Metastasising Pleomorphic Adenoma of the Parotid Gland: Where are We Now? A Systematic Literature Review.

Purpose: Metastasising pleomorphic adenoma (MPA) is a rare malignant tumour that can affect multiple organs with a considerable time latency compared to primary pleomorphic adenoma (PA). To date, MPA and its clinical course, including survival and relapse rates, are still poorly understood. Methods: We performed a systematic literature review following the PRISMA 2020 guidelines. The research was carried out using the PUBMED database and the following search terms: Results: A total of 908 papers were initially selected and 42 patients. The mean age at the diagnosis of MPA was 49.2 years (range 13-75 years). The average interval of onset of first metastasis was 15.7 years (range 1.4-45 years). The most common sites of metastasis were the bones (23.8%) and lungs (23.8%). In 31 patients (73.8%) a surgical treatment for complete removal of MPA was performed, while 10 patients withstood definitive or adjuvant radiotherapy. The follow up status was described only in 22 out of 40 papers where only 3 patients died from the neoplasm. Conclusion: MPA of the parotid gland is a rare condition. The transformation of a PA to MPA is unpredictable. Because of the scarcity of data in the literature, the long-term behaviour of metastatic neoplasm is uncertain. However, we found that 5 out of 19 patients experienced disease relapse after treatment. Additionally, the average survival rate for individuals with MPA of the parotid gland is 64% after 5 years. The preferred course of treatment, if possible, is the surgical removal of the neoplasm.