Brain Tumors: Types, Grades, and Multimodal Treatments Explained

When you hear the word brain tumor, it’s easy to picture the worst-case scenario: a fast-growing, untreatable mass. But the reality is far more nuanced. Brain tumors aren’t one thing-they come in many forms, grow at different speeds, and respond to different treatments. What matters most isn’t just the tumor’s location, but its type, its grade, and the molecular signals hidden inside its cells. Understanding these three things-type, grade, and treatment options-is the first step toward making sense of a diagnosis, whether you’re a patient, a caregiver, or someone just trying to learn.

What Are the Main Types of Brain Tumors?

Not all brain tumors are the same. They’re grouped by where they start and what kind of cell they come from. The most common types arise from glial cells-the support cells of the brain. These are called gliomas. Within that group, you’ll find astrocytomas, oligodendrogliomas, and glioblastomas. Each behaves differently.

Astrocytomas start in star-shaped cells called astrocytes. Some grow slowly, like pilocytic astrocytomas, which are almost always grade 1. Others, like diffuse astrocytomas, creep into healthy brain tissue and can turn into higher-grade tumors over time. Oligodendrogliomas come from a different kind of glial cell and often have a unique genetic signature: the loss of parts of chromosomes 1p and 19q. That’s not just a detail-it changes how they respond to treatment. Glioblastomas, the most aggressive form, are almost always grade 4 and grow so fast they create their own blood supply and leave dead tissue in the center.

Then there are meningiomas. These don’t start in brain tissue at all-they grow from the membranes covering the brain and spinal cord. Most are benign (grade 1), but some can become invasive. Even though they’re not technically brain tumors, they’re often treated the same way because they press on the brain and cause similar symptoms.

And then there’s the molecular layer. In the past, doctors looked only at what the tumor looked like under a microscope. Now, they test for specific gene changes. An astrocytoma with an IDH mutation behaves very differently from one without it-even if they look identical under the microscope. That’s why two grade 3 tumors might have totally different outcomes.

How Brain Tumors Are Graded: WHO CNS5 Explained

Grading tells you how aggressive a tumor is. The current system, called WHO CNS5, came out in 2021 and changed everything. Before this, grades were based mostly on how abnormal the cells looked. Now, molecular data is required to assign a grade. It’s no longer enough to say, “This is an anaplastic astrocytoma.” You have to say, “This is an astrocytoma, IDH-mutant, grade 3.”

Grade 1 tumors are the slowest. They look almost normal under the microscope and rarely spread. Pilocytic astrocytomas fall here. Surgery alone can often cure them.

Grade 2 tumors are low-grade but sneaky. They don’t look wildly abnormal, but they grow into nearby brain tissue. They can come back as higher-grade tumors years later. That’s why doctors monitor them closely-even if they don’t need treatment right away.

Grade 3 tumors are called anaplastic. The cells are actively dividing and invading. These are malignant. They need radiation and chemotherapy after surgery. Anaplastic astrocytomas and anaplastic oligodendrogliomas are in this group.

Grade 4 is the most dangerous. Glioblastoma, IDH-wildtype, is the most common type here. It grows fast, forms new blood vessels, and often comes back after treatment. Median survival is about 14.6 months with standard care. But if it’s IDH-mutant, survival jumps to over 31 months. That’s not a small difference-it’s life-changing.

The WHO CNS5 system also made grading type-specific. Meningiomas are graded 1 to 3, but they’re not compared to gliomas. Oligodendrogliomas only go up to grade 3-they don’t become grade 4. This shift means doctors can now predict behavior more accurately. A grade 3 oligodendroglioma isn’t as bad as a grade 3 astrocytoma. The system finally reflects biology, not just appearance.

Why Molecular Testing Changes Everything

Two tumors that look the same under a microscope can have completely different outcomes because of their genes. That’s why molecular testing isn’t optional anymore-it’s standard.

The key markers doctors test for are:

• IDH1 or IDH2 mutation: This tells you if the tumor has a metabolic change linked to slower growth. IDH-mutant tumors respond better to treatment and live longer.
• 1p/19q codeletion: This is a telltale sign of oligodendroglioma. Tumors with this change respond extremely well to chemotherapy, especially PCV (procarbazine, lomustine, vincristine).
• MGMT promoter methylation: This tells you if the tumor’s DNA repair system is turned off. If it is, temozolomide (a chemo drug) works much better.

Before 2021, these tests were optional. Now, they’re required to make a diagnosis. The FDA approved the Ventana IDH1 R132H antibody in 2021, cutting testing time from three weeks to under two days. That’s huge. It means patients get answers faster-and treatment starts sooner.

But there’s a catch. Not every hospital can do this testing. It requires specialized labs, trained pathologists, and expensive equipment. In community hospitals, patients may need to send samples to a reference lab. That adds days, sometimes weeks, to the diagnosis. And in some places, insurance doesn’t cover all the tests. That’s why many patients still wait too long for a full picture of their tumor.

How Brain Tumors Are Treated Today

Treatment isn’t one-size-fits-all. It’s a mix of surgery, radiation, chemotherapy, and sometimes new targeted drugs. The combination depends on the tumor’s type, grade, and molecular profile.

For grade 1 tumors, surgery is often enough. If the tumor is fully removed, no further treatment is needed. For grade 2 tumors, doctors may watch and wait, especially in younger patients. If it starts growing, they use radiation or chemo. Some grade 2 tumors, like IDH-mutant oligodendrogliomas, are now being treated with oral drugs like vorasidenib-approved by the FDA in June 2023. In the INDIGO trial, patients on vorasidenib went 27.7 months without their tumor growing, compared to 11.1 months on placebo.

For grade 3 and 4 tumors, the standard is the Stupp protocol: surgery, then radiation plus daily temozolomide for six weeks, followed by maintenance chemo for up to a year. But that’s not the whole story. If the tumor has MGMT methylation, temozolomide works better. If it’s an oligodendroglioma with 1p/19q codeletion, PCV chemo may be better than temozolomide. And for IDH-mutant glioblastomas, clinical trials are now testing drugs that target the IDH mutation directly.

There’s also emerging tech. Liquid biopsies-testing tumor DNA in spinal fluid-are showing promise. A 2023 study in Nature Medicine found they detected tumor DNA in 89% of cases. That could mean fewer invasive brain surgeries just to get tissue samples. And for patients who can’t have surgery, focused radiation like Gamma Knife or proton therapy offers precise alternatives with fewer side effects.

What Patients Are Really Facing

Behind every statistic is a person. A 32-year-old woman diagnosed with a grade 2 oligodendroglioma was told she had 72 hours to decide whether to freeze her eggs before surgery. A man with a grade 4 glioblastoma, told he had 14 months to live, joined a trial for vorasidenib and got 18 months without progression. That’s not just hope-it’s science working.

But the road isn’t smooth. A 2022 survey found 68% of patients waited more than eight weeks for a diagnosis. Low-grade tumor patients waited even longer-14 weeks on average. Many patients misunderstand what grade means. One in two thought grade 2 meant a 20% survival chance. It doesn’t. Grade 2 means slow-growing, not terminal.

Emotional toll is real. Anxiety, memory loss, fatigue, and the fear of recurrence are daily struggles. Support groups like the National Brain Tumor Society and Reddit’s r/BrainTumors community are lifelines. They help people navigate insurance, find clinical trials, and cope with the invisible symptoms no scan can show.

What’s Next for Brain Tumor Care?

The future is moving fast. The CODEL trial, testing combined chemo for oligodendroglioma, will release results in late 2024. New drugs targeting IDH mutations are in phase 3 trials. Liquid biopsies could replace invasive biopsies within five years. And AI tools are being trained to predict tumor behavior from MRI scans alone-without needing a tissue sample.

The WHO CNS5 system isn’t perfect. Dr. Kenneth Aldape from the National Cancer Institute admits that for some rare tumors, we still don’t know enough. But it’s the best tool we have. And it’s getting better every year.

What’s clear is this: brain tumors are no longer defined by what they look like. They’re defined by what they are at the molecular level. And that shift-from appearance to biology-is giving patients more precise answers, better treatments, and longer lives.