A glioma is a tumor that grows from glial cells, the supportive cells in the brain and spinal cord. Gliomas are the most common primary brain tumor, meaning they originate in the central nervous system rather than spreading there from another part of the body. They range widely in behavior, from slow-growing tumors that cause seizures but remain stable for years, to aggressive cancers that progress within months.
Where Gliomas Come From
Your brain contains billions of neurons, but neurons are actually outnumbered by glial cells. These supporting cells nourish neurons, maintain the chemical environment, and provide structural scaffolding. When glial cells grow abnormally, the resulting tumor is classified by which type of glial cell it resembles.
The three main types are:
- Astrocytomas: arising from star-shaped cells called astrocytes. These can range from slow-growing to extremely aggressive. Glioblastoma, the most well-known brain cancer, is a high-grade astrocytoma.
- Oligodendrogliomas: arising from oligodendrocytes, cells that produce the insulating coating around nerve fibers. These tend to be less invasive than astrocytomas and often respond better to treatment.
- Ependymomas: arising from cells that line the fluid-filled cavities of the brain and the central canal of the spinal cord. These are more common in young children.
How Gliomas Are Graded
The World Health Organization classifies gliomas into grades 1 through 4. Lower grades grow slowly and may remain relatively contained, while higher grades grow quickly and invade surrounding brain tissue. Grade 1 tumors are often well-defined and potentially curable with surgery alone. Grade 2 tumors grow slowly but tend to infiltrate nearby tissue, making complete removal difficult. Grade 3 tumors show clearly abnormal cells with more active division. Grade 4 tumors are the most aggressive, characterized by rapid growth, new blood vessel formation within the tumor, and areas of dead tissue at their core.
Modern classification doesn’t rely on microscope appearance alone. Molecular markers now play a defining role. A mutation in the IDH gene (found in many grade 2 and 3 gliomas) signals a fundamentally different and generally less aggressive disease than tumors without that mutation. Similarly, a specific genetic change called 1p/19q codeletion is required to diagnose an oligodendroglioma, and tumors carrying it tend to respond better to chemotherapy and carry a more favorable outlook. In some cases, molecular features can override what the tumor looks like under a microscope. An astrocytoma that appears low-grade on biopsy can be reclassified as grade 4 if it carries certain aggressive molecular signatures.
Common Symptoms
Seizures are the most frequent first symptom, particularly for lower-grade gliomas. Between 60% and 88% of people with grade 2 gliomas experience a seizure as their initial sign of the tumor. These are typically partial seizures, starting in one area of the brain and sometimes spreading. In more than half of cases, these seizures don’t respond well to standard anti-seizure medications.
Other symptoms depend on the tumor’s location and size. As a glioma grows, it compresses surrounding brain tissue, which can cause headaches (often worse in the morning), nausea, vision changes, or cognitive difficulties like trouble finding words or concentrating. Tumors in areas controlling movement may cause weakness on one side of the body. Personality or mood changes can occur when tumors affect the frontal lobe. High-grade gliomas tend to cause symptoms that worsen over weeks to months, while low-grade tumors may produce subtle symptoms for years before diagnosis.
Diagnosis
MRI is the primary imaging tool. It reveals the tumor’s size, location, and relationship to critical brain structures. Contrast dye injected during the scan highlights areas where the tumor has disrupted the normal blood-brain barrier, which generally indicates a higher-grade lesion. Advanced MRI techniques, including spectroscopy, can provide additional information about the tumor’s chemical makeup.
Imaging alone cannot confirm a glioma or determine its grade and molecular profile. A tissue sample is needed, obtained either through a targeted needle biopsy or during surgical removal of the tumor. Pathologists then examine the cells under a microscope and run molecular tests to identify mutations like IDH status and 1p/19q codeletion. These results determine the final diagnosis and directly shape treatment decisions.
Treatment Approaches
Surgery is almost always the first step. The goal is to remove as much tumor as possible while preserving brain function. For tumors near areas controlling speech, movement, or vision, surgeons may operate while the patient is awake to test those functions in real time. Even with a complete resection (removing everything visible on imaging), microscopic tumor cells almost always remain in the surrounding tissue. This is why additional treatment typically follows.
For high-grade gliomas, the standard approach after surgery combines radiation therapy with a chemotherapy drug called temozolomide, given at the same time, followed by additional cycles of temozolomide alone. For glioblastoma patients under 70 who are in good physical condition, a device that delivers low-intensity electrical fields to the scalp (tumor treating fields) may be added to this regimen. Another chemotherapy combination, called PCV, is commonly used for oligodendrogliomas and certain other glioma types.
Low-grade gliomas present a more nuanced treatment picture. If the tumor is small and was fully removed, close monitoring with regular MRI scans may be appropriate, particularly for grade 1 tumors. When additional treatment is needed, it typically involves radiation, chemotherapy, or both, but the timing can vary. Some patients are monitored for years before treatment beyond surgery becomes necessary.
Survival and Prognosis
Outcomes vary enormously depending on grade, molecular features, and how much tumor can be surgically removed. Five-year survival for grade 2 astrocytomas is roughly 61%. That drops to about 27% for grade 3 astrocytomas and around 11% for glioblastoma. These are population-level averages, and individual outcomes can differ significantly based on age, overall health, tumor location, and molecular markers.
Glioblastoma carries the most difficult prognosis. Average survival is 12 to 18 months after diagnosis with treatment. About 40% of patients are alive at one year and 17% at two years. If the tumor recurs after initial treatment, typical survival is 6 to 9 months. Tumors with IDH mutations, regardless of grade, generally carry a better prognosis than those without. Oligodendrogliomas with 1p/19q codeletion tend to have the most favorable outcomes among infiltrating gliomas, often responding well to chemotherapy for extended periods.
Known Risk Factors
For most people who develop a glioma, no clear cause is identified. The only well-established environmental risk factor is previous exposure to high-dose ionizing radiation to the head, such as radiation therapy for a prior cancer. This accounts for a small fraction of cases.
Several rare inherited genetic conditions significantly increase glioma risk. Neurofibromatosis type 1 predisposes people to astrocytomas and optic nerve gliomas. Li-Fraumeni syndrome, caused by mutations in the TP53 gene, raises the risk of glioblastoma along with many other cancers. Lynch syndrome, tuberous sclerosis, and neurofibromatosis type 2 also carry elevated risk for specific glioma types. These hereditary syndromes collectively explain only a small percentage of all gliomas. Researchers have identified common genetic variants that modestly increase risk in the general population, but no single gene or lifestyle factor accounts for most cases.