Metastasising pleomorphic adenoma: Systematic review

Area of Science:

• Oncology
• Pathology
• Surgical Oncology

Background:

• Pleomorphic adenoma (PA) is the most common benign salivary gland neoplasm.
• PA can rarely metastasize without apparent malignant transformation, termed metastasizing pleomorphic adenoma (MPA).
• MPA is histologically indistinguishable from PA but exhibits secondary tumor formation in distant sites.

Purpose of the Study:

• To conduct a comprehensive literature review of all reported MPA cases.
• To compile a virtual series of MPA cases for analysis.
• To investigate MPA demographics, metastatic patterns, prognosis, and treatment.

Main Methods:

• A PUBMED search was performed using keywords: metastasizing/metastasising AND pleomorphic adenoma OR mixed tumour.
• Included case reports from 1942 to 2014.
• An author's own case was incorporated into the review.

Main Results:

• Eighty case reports (1942-2014) plus one author's case were analyzed.
• Mean age at MPA diagnosis was 49.5 years; male-to-female ratio was 34:46.
• Mean time from PA to MPA was 14.9 years, with 72.8% having prior local PA recurrence. Common sites: bone (36.6%), lung (33.8%), neck lymph nodes (20.1%). 80.4% were alive at 1-year.

Conclusions:

• Metastasizing pleomorphic adenoma (MPA) is a rare entity.
• Metastasis typically occurs years after the initial PA diagnosis and is linked to multiple local recurrences.
• Despite a benign histological appearance, MPA demonstrates malignant metastatic behavior.