When people first hear they may have a brain mass, lesion, tumor, or even cancer, the terminology alone can feel overwhelming. As Dr. Jacob Young explains, “the terminology around this is actually pretty challenging because you’ll hear someone say a mass, you’ll hear somebody say a tumor, you’ll hear somebody say cancer. I think it’s understandably complex for patients to try to digest those different terms.”
Diffuse gliomas—one of the most common types of brain tumors—exist on a spectrum. Unlike many cancers, they rarely spread outside the brain, which is why doctors focus more on grade and molecular makeup rather than traditional cancer “stage.”
What Is a Diffuse Glioma?
Read MoreHow Diffuse Gliomas Are Graded
Doctors grade gliomas to better understand how the tumor behaves and to guide the safest, most effective treatment plan. A glioma’s grade reflects how fast the tumor is growing, how abnormal the cells look under a microscope, and how likely it is to spread within the brain. Lower-grade tumors tend to grow more slowly and may not need aggressive treatment right away, while higher-grade tumors grow faster and often require a combination of surgery, radiation, and chemotherapy. Grading gives doctors and patients a clearer picture of what to expect, helps predict outcomes, and ensures that care is tailored to the tumor’s specific biology.
Grading Diffuse Gliomas:
- Grade 1 – A slow-growing, usually well-defined tumor that often occurs in children; does not typically infiltrate the brain the way other gliomas do.
- Grade 2 – A slow-growing but diffuse (infiltrative) tumor; the tumor blends into normal brain tissue, so it can’t be fully removed by surgery.
- Grade 3 – A faster-growing, more aggressive diffuse glioma; usually requires a combination of surgery, radiation, and chemotherapy.
- Grade 4 – The most aggressive form, growing and invading quickly; Requires intensive treatment; prognosis depends on molecular features, patient age, and overall health.
Dr. Young explains, “when we think about diffuse gliomas, they can either be grade two, grade three or grade four… we have a pretty good sense if it looks like it’s going to be the more aggressive grade four variety… or the less aggressive lower grade, either two or three variety.”
What Pathologists Look For
Factors pathologist consider in evaluating diffuse gliomas include:
- Growth Rate
- Cell Presentation
- Genetic Mutations
- Tumor cell appearance
- Presence of any necrosis (dead cells in the tumor)
Determining whether a tumor is grade 2, 3, or 4 requires examining tissue under the microscope.
As Dr. Young notes, “grade two and grade three are also sort of on a continuum… the pathologists have to look under the microscope and tell us how many cells are dividing [and] if there’s evidence… that might push it from a grade two or a grade three.”
The Importance of IDH Mutation Status
An Isocitrate dehydrogenase (IDH) mutation is a small change in a gene that helps your cells make energy. When this gene is altered, it creates a chemical that shouldn’t be there — and that chemical can help certain brain tumors grow. Doctors check for an IDH mutation because it’s one of the most important clues about how the tumor will behave and which treatments may work best.
For more context: the IDH 1 and 2 codes for enzymes that are involved in cellular metabolism. However, when the IDH 1 or 2 gene is mutated and the enzyme is unable to function, there is a build up of a chemical that disrupts normal cell processes and contributes to brain tumor growth.
The gene is one of the most important markers in diagnosing diffuse gliomas today.
Dr. Young highlights its significance saying, “one of the key differentiations is whether these tumors have something called an IDH mutation… if there’s an IDH mutation present and it’s a diffuse glioma, they can no longer be considered glioblastomas, but they can still be grade four tumors.”
This means a tumor can look aggressive under the microscope yet behave differently depending on its genetics.
Putting It All Together: How Doctors Look at the Big Picture
There is no single feature that determines a glioma’s grade. Instead, doctors evaluate:
- How the tumor cells look
- How quickly they are dividing
- Whether necrosis or microvascular proliferation is present
- The tumor’s genetic profile, including IDH and other mutations
As Dr. Young summarizes, “it’s a combination of the appearance under the microscope, the genetic profile and certain mutations that are present.”
What Patients Should Ask Their Doctor
When facing a glioma diagnosis, understanding the big picture can help guide decision making. Consider asking your doctor:
- What grade is my tumor, and what features support that grade?
- Does my tumor have an IDH mutation or other genetic markers?
- How does my tumor’s molecular profile affect treatment options?
- How aggressive does this appear based on imaging and pathology?
- What is the recommended treatment plan for my specific tumor type and grade?
- How will we monitor for progression over time?
These questions can clarify expectations and help you take an active role in your care.
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