Glioblastoma multiforme metastasis to the parotid gland : a systematic review of case series and case studies

Abstract

Introduction: Glioblastoma multiforme (GBM) is a highly aggressive, IDH-wildtype grade IV brain tumor with rapid growth, invasiveness, and poor prognosis despite treatment. Extra-neural glioblastoma (GBM) metastasis to the parotid gland is exceedingly rare and inadequately documented.

Methods: A systematic review following PRISMA2020 guidelines for case-reports or case-senes documenting histologically confirmed GBM metastasis to the parotid gland was conducted for studies published until 01/05/2024 (CRD42024517593).

Results: 13 studies were included, with general good reporting quality. Average age on GBM diagnosis was 42.73 years (range: 25 - 58 years), with metastasis occurring after 9.77 months (range: 2.5 - 24 months). 8 patients had intracranial GBM metastasis and 9 had additional extra-neural metastasis, 7 being lymph-nodes. Frontal lobe and temporal lobe GBM involvement was noted in five tumours respectively, with two involving the parotid and one the occipital lobe. All parotid metastases were ipsilateral to the site of the original GBM tumour. All patients underwent resection and postoperative radiotherapy for their primary tumours.

Discussion: GBM metastasis to the parotid gland is exceedingly rare and occurred in younger individuals, with all documented cases showing ipsilateral spread which may suggest a pattern of lymphatic spread, though the limited data makes this challenging to confirm definitively. Additional research and case documentation are necessary to better understand the mechanisms and pathways of extra-neural metastasis, particularly to the parotid gland.