Glioblastoma, also called GBM, is the most aggressive primary brain cancer. It carries a WHO grade 4 classification, the highest possible malignancy grade, and has a median survival of roughly 14 months even with modern treatment. Without treatment, it can be fatal in fewer than six months. Around 90% of cases recur after initial treatment, and fewer than 10% of patients survive five years.
What Makes Glioblastoma So Aggressive
Several biological traits set GBM apart from other brain tumors. The cancer cells grow and multiply faster than any other type of astrocytoma, which is the broader category of tumors that arise from star-shaped brain cells called astrocytes. But speed alone doesn’t explain GBM’s lethality. The tumor infiltrates surrounding healthy brain tissue in a way that makes its edges impossible to clearly distinguish from normal tissue. A surgeon removing a GBM can never be certain every cancer cell has been taken out, because the tumor’s margins blur into functioning brain.
GBM also excels at building its own blood supply. The tumor hijacks existing blood vessels and triggers the growth of new ones, a process driven by low oxygen levels within the tumor itself. As the tumor outgrows its blood supply, pockets of dead tissue (necrosis) form at its core. These oxygen-starved zones then send chemical signals that stimulate even more blood vessel growth around the tumor’s edges, fueling further expansion. This cycle of death, oxygen deprivation, and new vessel formation is one of GBM’s signature characteristics and a major reason it resists treatment so effectively.
How GBM Is Diagnosed
Under the 2021 WHO classification, a tumor qualifies as glioblastoma when it meets two conditions: it lacks mutations in a gene called IDH (making it “IDH-wildtype”), and it shows specific hallmarks visible under a microscope or through genetic testing. Those hallmarks include abnormal blood vessel growth, necrosis, or certain molecular markers like mutations in the TERT gene promoter, amplification of the EGFR gene, or a characteristic pattern of gaining chromosome 7 while losing chromosome 10.
What’s notable is that even tumors that look less aggressive under a microscope can be classified as grade 4 glioblastoma if they carry those molecular markers. This means a biopsy that might once have been labeled a lower-grade tumor now gets the GBM diagnosis based on its genetic fingerprint, reflecting how the tumor will actually behave.
Symptoms and How Quickly They Appear
GBM symptoms tend to come on quickly, often over days to weeks rather than months. The specific symptoms depend on where in the brain the tumor is growing, but common early signs include new or worsening headaches, seizures (sometimes as the very first symptom), memory problems, vision changes, and progressive weakness or numbness on one side of the body. Some people notice personality changes or difficulty finding words. Unexplained nausea and vomiting can also occur as the tumor raises pressure inside the skull.
Because these symptoms overlap with many less serious conditions, the rapid onset and progressive worsening are the key warning signs. A headache that gets steadily worse over a couple of weeks, especially paired with a new seizure or cognitive changes, warrants urgent imaging.
Standard Treatment and What to Expect
The standard approach for newly diagnosed GBM, known as the Stupp protocol, combines surgery, radiation, and chemotherapy. Surgery removes as much of the tumor as safely possible, though complete removal is essentially impossible due to the infiltrating nature of the cancer. After surgery, patients receive about six weeks of daily radiation (totaling 60 Gy) alongside a daily oral chemotherapy drug. This is followed by six additional monthly cycles of chemotherapy alone.
A newer addition to the treatment toolkit is a wearable device that delivers low-intensity electric fields to the scalp, called Tumor Treating Fields. In a randomized clinical trial published in JAMA, patients who used this device alongside chemotherapy had a median survival of 20.9 months from randomization, compared to 16.0 months for chemotherapy alone. Progression-free survival also improved, from 4.0 to 6.7 months. The device is worn for most of the day and works by disrupting cell division in rapidly growing tumor cells.
Why Recurrence Is Nearly Universal
Despite aggressive first-line treatment, roughly 90% of GBMs come back. The median time to recurrence is around eight months after initial treatment. Recurrence happens because microscopic cancer cells left behind after surgery continue to grow, and they often develop resistance to radiation and chemotherapy over time. When GBM recurs, treatment options become more limited and less effective, and survival after recurrence is typically measured in months.
Survival by the Numbers
In clinical trial populations, where patients tend to be younger and healthier, median overall survival reaches 15 to 18 months. In real-world settings, outcomes are often worse. One retrospective study found a median survival of 10 months, with one-year survival at 30% and two-year survival at just 6.7%. Reports of patients surviving beyond five years exist but are rare enough to be considered sporadic. Age at diagnosis, the extent of surgical removal, and the tumor’s molecular profile all influence where an individual falls within these ranges.
DIPG: The Most Aggressive Brain Cancer in Children
In children, the most aggressive brain cancer is diffuse intrinsic pontine glioma, or DIPG. This tumor grows in the brainstem, a location that makes surgery impossible. DIPG accounts for 10% to 20% of all childhood brain tumors and carries a median survival of less than 12 months. Only about 10% of children with DIPG survive two years or longer. Radiation can temporarily slow growth and relieve symptoms, but no chemotherapy regimen has proven effective, and the prognosis has barely improved over several decades.
Newer Treatment Approaches
One of the more promising experimental strategies involves engineering a patient’s own immune cells to recognize and attack tumor cells, a technique called CAR-T cell therapy. Early-phase trials have tested immune cells programmed to target a protein called B7-H3, which is found on GBM and DIPG cells. In one trial, half of the patients showed at least 30% tumor shrinkage, and 75% had stable disease at least two months after treatment. The therapy was delivered directly into the brain or spinal fluid rather than intravenously, and early safety data showed no dose-limiting toxicity after 40 infusions in the first patients treated.
These results are preliminary, from small groups of patients in phase I trials designed primarily to test safety. But the fact that any measurable tumor shrinkage occurred in a cancer this resistant to treatment has generated significant interest. Additional trials targeting other surface proteins on GBM cells are underway.