After "what type is it?", the next question is almost always "what grade is it?" Grade is one of the most important — and most misunderstood — parts of a glioma diagnosis.
Grade is an estimate of how a tumor tends to behave It is based on how the tumor cells look and, increasingly, on molecular features. The World Health Organization uses grades from 1 to 4:
- Grade 1 tumors are the slowest-growing and most contained. Some can be cured with surgery alone. Many grade 1 gliomas occur in children.
- Grade 2 tumors grow slowly but tend to spread into surrounding brain tissue and can change into higher grades over time.
- Grade 3 tumors grow more actively and usually need treatment beyond surgery.
- Grade 4 tumors, including glioblastoma, are the fastest-growing and most aggressive.
A common shorthand divides gliomas into low-grade (roughly grades 1–2) and high-grade (grades 3–4). This is useful, but it is a simplification.
Two updates from modern classification are worth knowing. First, grade is no longer purely about appearance. A glioma can be assigned a higher grade based on specific gene changes even without the classic aggressive look under the microscope — for example, an *IDH*-mutant astrocytoma with a change called CDKN2A/B deletion is now graded 4. Second, grade is read alongside type and molecular markers, not in isolation. A grade 3 oligodendroglioma and a grade 3 astrocytoma can have meaningfully different outlooks.
The patient-friendly message: grade tells you something important about how urgently and aggressively a tumor usually needs to be treated, but your tumor's grade is only one ingredient. Ask your team to explain your grade together with your tumor type and molecular results, because that combination — not the number alone — is what guides your care.