Glioblastoma is the most common and most aggressive primary brain cancer in adults. It carries a median survival of roughly 12 to 15 months after diagnosis and a five-year survival rate below 10%, even with treatment. The tumor grows and spreads quickly within the brain, making complete removal nearly impossible. Understanding what glioblastoma is, how it behaves, and what treatment looks like can help make sense of a diagnosis that often feels overwhelming.
Where Glioblastoma Starts
Glioblastoma develops from cells in the brain’s supporting tissue, not from neurons themselves. Current research points to neural stem cells and glial precursor cells as the likely cells of origin. These are immature cells that normally develop into the glial cells responsible for insulating and nourishing neurons. When genetic mutations cause them to grow uncontrollably, the result is a fast-growing, highly invasive tumor.
One defining feature of glioblastoma is its internal variety. Under a microscope, the tumor contains a chaotic mix of cell shapes and sizes, areas of new blood vessel growth, and zones of dead tissue (necrosis). This heterogeneity is part of what makes glioblastoma so difficult to treat: different parts of the same tumor can behave differently and respond differently to therapy.
How It Is Classified
The World Health Organization updated its brain tumor classification system in 2021, and the change matters for glioblastoma specifically. Under the current system, the term “glioblastoma” is reserved exclusively for tumors that are IDH-wildtype, meaning they lack a specific mutation in the IDH gene. Tumors that do carry an IDH mutation are now classified as a separate type (astrocytoma, IDH-mutant) even if they look similar under a microscope. This distinction is important because IDH-mutant tumors generally have a better prognosis.
Glioblastoma is graded as CNS WHO grade 4, the highest grade. A tumor can receive this designation based on its microscopic appearance (new blood vessel growth or necrosis) or based on certain genetic markers alone, even if the tissue doesn’t look as aggressive under a microscope. Three genetic markers can independently qualify a tumor for a grade 4 diagnosis: a mutation in the TERT promoter, amplification of the EGFR gene, or a specific pattern of chromosome gains and losses known as +7/−10.
Who Gets Glioblastoma
Glioblastoma affects about 3.2 people per 100,000 in the United States each year. The median age at diagnosis is 64, and the cancer is uncommon in children. Men are diagnosed slightly more often than women. Unlike some cancers with clear lifestyle risk factors, the causes of glioblastoma remain largely unknown. Prior radiation exposure to the head is one of the few established risk factors, and most cases occur without any identifiable cause.
Common Symptoms
Symptoms depend on where in the brain the tumor grows, but certain patterns are common. The tumor increases pressure inside the skull, which often produces persistent headaches, nausea or vomiting, and seizures. These are frequently the symptoms that first bring someone to medical attention.
Beyond those general signs, glioblastoma can cause focal neurological problems tied to its location. A tumor in the frontal lobe may cause personality changes, difficulty planning, or memory problems. Tumors near speech areas can produce trouble finding words or understanding language. Weakness on one side of the body, vision changes, balance problems, and confusion are all possible. In some cases, cognitive and behavioral changes develop so gradually that they’re initially mistaken for depression or dementia, delaying diagnosis until the tumor is quite large.
When symptoms raise suspicion of a brain tumor, an MRI scan is the primary diagnostic tool. Glioblastomas typically appear as large, irregularly shaped masses with areas of contrast enhancement and central necrosis. A tissue biopsy, usually obtained during surgery, confirms the diagnosis and provides the molecular information needed to guide treatment.
Standard Treatment
Treatment follows a well-established three-phase approach. The first step is surgery to remove as much of the tumor as safely possible. Because glioblastoma infiltrates surrounding brain tissue with finger-like projections, surgeons can rarely remove it entirely. The goal is to reduce the tumor’s bulk, relieve pressure symptoms, and obtain tissue for diagnosis.
After surgery, patients begin a combination of radiation and chemotherapy that lasts about six weeks. Radiation is delivered in 30 sessions over that period, while a chemotherapy drug is taken daily alongside it. Following this combined phase, chemotherapy continues on its own in monthly cycles for six additional months, sometimes extended up to twelve months at the treating doctor’s discretion. This regimen has been the backbone of glioblastoma treatment since 2005.
An additional treatment option called Tumor Treating Fields uses a portable device that delivers low-intensity electrical fields to the scalp through adhesive arrays. These electrical fields interfere with the internal machinery cancer cells need to divide, disrupting the assembly of structural proteins during cell division and causing dividing cells to die. Because healthy brain cells divide far less frequently, they are largely spared. When added to standard chemotherapy, this approach improved the five-year survival rate from 5% to 13% in clinical trials.
What Affects Survival
Several factors influence how long someone lives with glioblastoma. Age at diagnosis, overall health, and how much tumor can be safely removed during surgery all play a role. But one of the strongest biological predictors is the methylation status of a gene called MGMT.
The MGMT gene produces a protein that repairs a specific type of DNA damage, the same type of damage that chemotherapy is designed to inflict on cancer cells. When the MGMT gene’s control switch (its promoter) is chemically silenced through a process called methylation, the cancer cells lose their ability to repair chemotherapy damage, making the treatment far more effective. Patients with a methylated MGMT promoter had a median survival of about 504 days (roughly 16.5 months), compared to 329 days (about 11 months) for those without methylation. In younger patients under 53, this gap widened further: 639 days versus 433 days. MGMT status is now routinely tested after biopsy because it is the strongest predictor of how well a patient will respond to chemotherapy.
Recurrence
Glioblastoma almost always comes back. The average time before the tumor begins growing again is approximately seven months from diagnosis. When recurrence happens, the outlook is difficult: median survival after recurrence is less than one year.
There is no established standard of care for recurrent glioblastoma. Options include a second surgery if the tumor is accessible, additional radiation, or systemic therapies. These systemic treatments include different chemotherapy drugs, drugs that block blood vessel growth to the tumor, and targeted therapies. All of these are considered palliative, meaning they aim to control the disease and maintain quality of life rather than cure it. None has been proven superior to the others, so treatment decisions are highly individualized.
Experimental Therapies
One of the most active areas of glioblastoma research involves engineering a patient’s own immune cells to attack the tumor. In this approach, immune cells are removed from the blood, genetically modified in a lab to recognize specific proteins on glioblastoma cells, and then infused back into the patient, sometimes directly into the brain. Early-phase clinical trials have shown that these engineered cells can reach the tumor and produce measurable responses. In one trial of 65 patients, half achieved disease control and 23% survived at least one year. Newer versions target two tumor proteins simultaneously to reduce the chance of the cancer evolving to escape recognition.
Another experimental strategy pairs these engineered immune cells with a vaccine designed to amplify their activity inside the tumor. The vaccine uses messenger RNA technology to prompt the body to produce more of the protein the immune cells are trained to attack, essentially giving them a stronger signal to follow. These approaches remain in early testing, and none are yet approved as standard treatment, but they represent a fundamentally different strategy from the surgery-radiation-chemotherapy model that has defined glioblastoma care for two decades.