Glioblastoma is the most common and most aggressive form of brain cancer, accounting for nearly half of all malignant brain tumors. It carries a median survival of roughly 9 to 15 months depending on treatment, and it strikes about 3.2 people per 100,000 each year. The median age at diagnosis is 65, though it can occur at any age.
Where Glioblastoma Starts
Glioblastoma grows from glial cells, the support cells of the brain that surround and protect neurons. For years, researchers assumed it always started in a specific type of glial cell called an astrocyte. More recent evidence shows it can also arise from neural stem cells or from earlier-stage cells called glial progenitors. Under a microscope, the tumor is made up of cells that resemble immature versions of several glial cell types, which is part of what makes it so unpredictable.
The World Health Organization classifies glioblastoma as a grade 4 brain tumor, the highest grade. Grade 4 means the cells are dividing rapidly, the tumor generates its own blood supply, and areas of dead tissue (necrosis) form at its core. Unlike lower-grade brain tumors that may grow slowly over years, glioblastoma can double in size within weeks.
Common Symptoms
Symptoms depend heavily on where in the brain the tumor forms. Some people first notice frequent or worsening headaches, particularly headaches that are worse in the morning or when lying down. Others experience new seizures with no prior history of epilepsy. Nausea and vomiting can accompany the headaches as pressure builds inside the skull.
Because glioblastoma can appear in almost any part of the brain, it also causes location-specific problems: difficulty speaking, vision changes, weakness on one side of the body, trouble with balance, or changes in sensation. Cognitive symptoms are common too, including confusion, memory loss, difficulty concentrating, personality changes, and irritability. These symptoms often develop over days to weeks, not months, reflecting the tumor’s fast growth.
How It’s Diagnosed
MRI is the primary imaging tool. On a contrast-enhanced MRI, glioblastoma has a distinctive appearance: a mass with a bright, irregularly enhancing rim surrounding a dark center of dead tissue. This “ring-enhancing” pattern, combined with surrounding brain swelling, is characteristic enough that radiologists can often suspect glioblastoma before surgery. A tissue sample (biopsy), usually obtained during surgical removal, confirms the diagnosis.
Two molecular markers matter for prognosis and treatment planning. The first is IDH mutation status. Most glioblastomas are “IDH-wildtype,” meaning the IDH gene is normal. The small percentage with an IDH mutation tend to have significantly better outcomes. The second marker involves a gene called MGMT, which produces a protein that repairs DNA damage caused by chemotherapy. When the MGMT gene is silenced through a chemical process called promoter methylation, the tumor is less able to repair chemotherapy damage, and treatment works better.
These two markers together create a wide spectrum of expected outcomes. Patients whose tumors carry both an IDH mutation and MGMT silencing have a median survival around 36 months with standard treatment. Those with neither favorable marker have a median survival closer to 15 months.
Standard Treatment
Treatment follows a well-established sequence known informally as the Stupp protocol, named after the oncologist who designed the landmark trial. It has three phases: surgery, then combined radiation and chemotherapy, then chemotherapy alone.
Surgery comes first. The goal is to remove as much tumor as safely possible without damaging critical brain areas that control speech, movement, or other essential functions. There is no universally agreed-upon percentage of tumor that must be removed for surgery to be worthwhile. Surgeons use real-time brain mapping and intraoperative MRI to push the boundaries of what can be safely taken out, because more complete removal is consistently linked to longer survival.
About four weeks after surgery, patients begin six weeks of daily radiation combined with a daily oral chemotherapy pill. The chemotherapy is taken every day during this phase, including weekends. After a four-week break, patients then take the same chemotherapy at a higher dose for five days out of every 28-day cycle, continuing for six cycles total. This entire treatment timeline spans roughly nine to ten months from the start of radiation.
Tumor Treating Fields
A newer addition to the treatment toolkit uses a wearable device that delivers low-intensity alternating electric fields to the scalp. These fields interfere with cell division by disrupting the internal scaffolding that cancer cells need to split into two daughter cells. The result is that dividing tumor cells stall mid-division and die, while non-dividing healthy brain cells are largely unaffected. The device also appears to make the blood-brain barrier temporarily more permeable, potentially helping chemotherapy reach the tumor more effectively.
The catch is compliance. The device needs to be worn for at least 18 hours per day to be effective. In clinical trials, patients who wore it 75% of the time or more (at least 18 hours daily) had a median survival of 7.7 months when used alone for recurrent glioblastoma, compared to 4.5 months for those with lower compliance. It is now commonly used alongside standard chemotherapy for newly diagnosed patients as well.
When the Tumor Comes Back
Glioblastoma recurs in nearly all cases. The median time before progression on standard treatment ranges from about 7 to 10 months. Recurrence typically happens near the original tumor site, though it can appear anywhere in the brain.
One complication in monitoring is a phenomenon called pseudoprogression. In the weeks after completing radiation and chemotherapy, MRI scans sometimes show what looks like tumor growth but is actually treatment-related inflammation. If the apparent growth stabilizes without any change in treatment over the next six months, it’s reclassified as pseudoprogression rather than true recurrence. Distinguishing the two is critical because they lead to very different decisions.
For true recurrence, options become more limited. A chemotherapy drug called lomustine is widely used and has been an approved treatment for recurrent glioblastoma for decades. A blood vessel-blocking drug called bevacizumab received FDA approval for recurrent glioblastoma in 2009. It works by cutting off the tumor’s blood supply, which can reduce swelling and improve symptoms, though its effect on overall survival remains debated. Combinations of the two have shown some encouraging results. Repeat surgery is sometimes an option if the tumor is accessible. Many patients at this stage also consider clinical trials testing newer approaches.
Survival and Prognosis
The overall median survival from diagnosis is roughly 9 to 15 months, with the range depending on treatment intensity and tumor biology. About 41% of patients survive one year, and around 13% survive two years. Five-year survival remains rare, in the single digits for most studies.
Several factors influence where an individual falls on this spectrum. Younger age, better functional status at diagnosis, more complete surgical removal, MGMT silencing, and IDH mutation all tilt the odds toward longer survival. Among patients with none of these favorable factors, those treated with radiation alone had a median survival of 9.6 months. Adding chemotherapy to radiation pushed that to 15.4 months, a meaningful but sobering improvement. For the small group with both IDH mutation and MGMT silencing, median survival stretched beyond three years, illustrating just how much tumor biology matters.