Metastasizing Pleomorphic Adenoma: A Systematic Review and Pooled Case-Report Analysis

Area of Science:

• Oncology
• Pathology
• Surgical Oncology

Background:

• Metastasizing pleomorphic adenoma (MPA) is a rare salivary gland tumor with benign morphology but metastatic potential.
• Existing evidence is largely based on case reports and small series, necessitating a comprehensive review of patient-level data.

Purpose of the Study:

• To systematically review and pool published patient data on MPA.
• To explore clinicopathologic features, metastatic patterns, treatment strategies, and survival outcomes.
• To identify areas for future research and improved management.

Main Methods:

• Systematic literature search of PubMed, Scopus, and Google Scholar up to August 2025.
• Pooled analysis of 122 published case-report patients with MPA (excluding malignant variants).
• Exploratory survival analyses using Kaplan-Meier and univariable Cox models due to limited death data.

Main Results:

• The majority of primary tumors arose in the parotid gland (75.4%).
• Common metastatic sites included bone/skeleton and lymph nodes/neck (35.0% each), followed by lung (25.8%).
• Surgery was associated with improved overall survival (log-rank p=0.008), though this finding is exploratory.

Conclusions:

• MPA is challenging to predict, with evidence limited by study design and data heterogeneity.
• Surgical management may be considered for selected MPA patients, but the survival association requires cautious interpretation due to potential biases.
• Multicenter registries, standardized reporting, and molecular characterization are crucial for advancing MPA understanding and treatment.