Glioblastoma Multiforme

Glioblastoma is the most common and most aggressive primary malignant brain tumor in adults, an infiltrating astrocytic glioma classified as central nervous system WHO grade 4. It diffusely invades surrounding brain, which makes complete surgical removal impossible and underlies its characteristically poor prognosis despite multimodal treatment.

Definition

Glioblastoma is a diffusely infiltrating, IDH-wildtype astrocytic glioma of central nervous system WHO grade 4, defined by its astrocytic lineage together with characteristic molecular features and, classically, histological hallmarks of microvascular proliferation and necrosis.

Scope

The entry covers glioblastoma as a defined tumor entity: its place in the molecular classification of gliomas, its infiltrative biology, the rationale for combining surgery, radiotherapy, and chemotherapy, and the prognostic markers that refine its categorization. It is a reference description of the disease, not treatment guidance.

Core questions

• Why does the infiltrative nature of glioblastoma make surgical cure unattainable?
• How did molecular markers such as IDH status and MGMT promoter methylation reshape its definition and prognosis?
• What is the evidence basis for combining radiotherapy with temozolomide?
• How is grade 4 distinguished from lower-grade diffuse gliomas?

Key concepts

• Diffuse infiltration of brain parenchyma
• IDH-wildtype status
• Central nervous system WHO grade 4
• MGMT promoter methylation
• Microvascular proliferation and necrosis
• Maximal safe resection
• Concurrent chemoradiotherapy

Mechanisms

Glioblastoma cells migrate along white matter tracts and perivascular spaces far beyond the imaging-visible tumor margin, so that microscopic disease remains after even a gross-total resection and recurrence is the rule. The tumor is highly vascular, with abnormal proliferating microvasculature and regions of necrosis that are histological hallmarks. The 2021 WHO classification defines adult glioblastoma as an IDH-wildtype diffuse astrocytic tumor and incorporates molecular criteria so that certain genetic features establish grade 4 even without classic histology. Epigenetic silencing of the MGMT DNA-repair gene by promoter methylation impairs repair of alkylator-induced damage and is associated with greater benefit from temozolomide.

Clinical relevance

Glioblastoma exemplifies how an infiltrative malignant glioma is conceptualized, classified, and studied, and how landmark trials established the combined-modality framework now used as a reference standard. This entry describes the disease and the evidence around it for educational orientation and is not a basis for individual diagnostic or treatment decisions.

Epidemiology

Glioblastoma is the most frequent malignant primary brain tumor in adults, with incidence rising with age and a median age at diagnosis in older adulthood; population-based registries describe its distribution among central nervous system tumors. Even with maximal treatment, reported median survival remains limited, reflecting its aggressive biology.

Evidence & guidelines

The pivotal EORTC-NCIC trial reported by Stupp and colleagues established radiotherapy with concurrent and adjuvant temozolomide as a reference regimen, with the 5-year analysis confirming a survival benefit concentrated in tumors with a methylated MGMT promoter. The 2021 WHO classification provides the current diagnostic framework, and EANO guidelines synthesize diagnosis and management of adult diffuse gliomas.

History

Once defined by histology alone as a glioblastoma multiforme, the entity was progressively redefined by molecular biology. The 2005 Stupp trial established chemoradiotherapy as a standard of care, and successive WHO classifications, culminating in 2021, reframed glioblastoma as a molecularly defined IDH-wildtype grade 4 astrocytoma, retiring the older purely morphological designation.

Debates

How should the extent of surgical resection be balanced against neurological risk?

Greater extent of resection is associated with better outcomes, but glioblastoma's infiltration into and near eloquent regions means the goal is maximal safe resection rather than radical removal, and the optimal balance remains a clinical judgement.

How decisive is MGMT promoter methylation for treatment choices?

Methylation status predicts benefit from temozolomide and is widely used in prognostication, but how strictly it should guide treatment, particularly in older or unmethylated patients, continues to be discussed.

Key figures

• Roger Stupp
• Monika E. Hegi
• David N. Louis
• Michael Weller

Seminal works

• stupp-2005
• stupp-2009
• louis-2021

Frequently asked questions

Why can glioblastoma not be cured by surgery alone?

Because the tumor diffusely infiltrates surrounding brain well beyond what imaging shows, microscopic tumor cells remain after surgery, so resection is combined with radiotherapy and chemotherapy rather than relied upon alone.

What does MGMT promoter methylation indicate?

It is an epigenetic marker that impairs a DNA-repair enzyme; tumors with a methylated MGMT promoter tend to respond better to the alkylating chemotherapy temozolomide and carry a relatively more favorable prognosis.