glioblastoma
Meaning of glioblastoma: What makes it so hard to remove is not its size but its edges, which merge into brain that looks and behaves normally.
Definition of glioblastoma
Glioblastoma is a fast-growing cancer of the brain arising from glial cells, the supporting tissue that surrounds and maintains neurons. It is graded 4, the highest grade among diffuse gliomas, and current classification reserves the name for tumors carrying no mutation in the IDH gene. It sends fine extensions into surrounding brain rather than forming a discrete lump.
How is it classified?
Gliomas are ranked from grade 1 to grade 4 by how abnormal their cells look and how fast they divide, and the highest grade belongs to this tumor. Classification no longer rests on appearance alone. A diffuse astrocytic tumor in an adult is called glioblastoma only when molecular testing shows no IDH mutation; a tumor of the same grade that does carry one is named astrocytoma, IDH-mutant, grade 4, tends to occur in younger adults, and progresses more slowly. The older term glioblastoma multiforme has been dropped, and grades are written in Arabic numerals. Most cases arise without any preceding lower-grade tumor, appearing at full aggression from the outset.
What does it look like?
| Seen by | Characteristic findings |
|---|---|
| Microscope | Crowded, highly irregular cells; abnormal proliferating vessels; dead areas with cells palisaded around them |
| Imaging | A thick irregular enhancing rim, a necrotic center, and extensive surrounding swelling |
| Molecular profile | IDH-wildtype, with changes including TERT promoter mutation and EGFR amplification |
The variety of appearances within a single tumor is what earned it the original name, and it is also why a small sample can under-represent the whole; grading depends on finding the most abnormal region.
Why does it return where it started?
Its cells migrate, but they migrate within the nervous system, travelling along white matter tracts and around vessels, occasionally crossing to the opposite hemisphere through the connecting fibers. They almost never leave to seed other organs, which is unusual for so aggressive a brain tumor. The consequence is that disease reliably reappears close to the original site, and treatment is planned around that: the largest safe surgical removal, then radiation therapy to the surgical bed with a margin, with chemotherapy given alongside and continued afterward. A wearable device delivering alternating electric fields to the scalp is a further option used after radiation.
Also known as
Used in a sentence
The patient underwent surgical resection followed by radiation therapy for a diagnosed glioblastoma.
Good to know
Glioblastoma is separated from lower-grade astrocytomas by its grade and growth pattern, and current classification also requires that no IDH mutation be present, since IDH-mutant grade 4 astrocytomas are named separately and behave differently.
Word origin
Where “glioblastoma” comes from
Formed from glio-, from Greek glia, meaning glue, referring to the glial cells of origin, combined with blastos, meaning germ or bud, and -oma, meaning tumor.