Glioblastoma (overview)

What it is

Glioblastoma is the most aggressive and most common malignant primary brain tumor in adults. In the modern classification, it is defined as an IDH-wildtype, grade 4 diffuse astrocytic glioma — meaning it lacks the IDH mutation and has features (or molecular markers) of grade 4 aggressiveness.

Understanding Glioblastoma (overview)

Glioblastoma grows rapidly and infiltrates surrounding brain tissue extensively, which makes it very difficult to remove completely and prone to recurrence. Under WHO CNS5, the term "glioblastoma" is reserved for IDH-wildtype tumors; a grade 4 tumor with an IDH mutation is instead called "astrocytoma, IDH-mutant, grade 4." Glioblastoma can be diagnosed by aggressive microscopic features (such as microvascular proliferation or necrosis) or by certain molecular markers (TERT promoter mutation, EGFR amplification, or +7/−10) even without those microscopic features. Standard treatment is intensive — surgery, radiation, and chemotherapy, often with additional therapies — and although the outlook has historically been poor, research into new treatments is very active. Understanding glioblastoma clarifies the most aggressive glioma and its modern, molecularly based definition.

Why it matters

Understanding glioblastoma helps patients and families grasp the most aggressive glioma and its modern definition — recognizing that treatment is intensive and that research into better therapies is ongoing, while outcomes are best discussed individually with the care team.