Glioblastoma

One growth story explains the necrosis, the ring on the scan, and the swelling. And it explains why the tumor keeps coming back. Plus why a tumor that did not look grade 4 is still called this. And what happened to secondary glioblastoma.

The short version

One thing this tumor does explains most of what you will be told about it. It grows faster than it can build a blood supply, so the middle of it starves and dies. That dead area is why your scan report says necrosis, why the tumor shows up as a bright ring with a dark center, why there is swelling around it, and why it keeps pushing outward. glioblastoma: A glioma that is given grade 4. Grade 4 is the highest grade there is. The tumor grows fast. Treatment usually starts soon after it is found. It often means surgery, and then radiation and chemotherapy. See the glossary and glioblastoma multiforme are older words for the same tumor. If your paperwork says secondary glioblastoma, look for the IDH gene change: A small change in a tumor's IDH gene. It is the first thing your team looks at when naming an adult glioma, and it can affect which treatments are offered. Your pathology report says whether your tumor has it. See the glossary line on your report: it decides whether this page is yours or whether astrocytoma is.

What is a glioblastoma?

A glioblastoma is a tumor that starts in the brain's helper cells, the ones that sit around and support nerve cells. It is one kind of glioma, and it is the most common cancerous brain tumor that starts in the brain in adults.

It is described as having poorly defined boundaries. That is not a detail about the scan. It is the single most important fact about this tumor, and most of this page follows from it.

GBM, and the older name glioblastoma multiforme

You will see three words used for one thing.

They are the same diagnosis. Nothing about your tumor is different depending on which one somebody uses.

Is it cancer? What does its grade mean?

Yes. A glioblastoma is cancer. The word your team will use is malignant.

It is always grade 4. There is no grade 1, 2 or 3 glioblastoma. Grade 4 is the top of the scale, and it describes how the cells look and behave rather than how long anybody has. If you have been told "glioblastoma", you have been told grade 4 at the same time, whether or not the number was said out loud.

Grade 4 is not a prediction about you. It is a description of the tumor.

But my tumor did not look grade 4

This catches a lot of people out, and it is not a mistake.

Since 2021, a tumor can be called a glioblastoma on its gene results alone. That holds even when the cells under the microscope look like a lower grade.

The rule is this. The tumor has no IDH change, and it carries at least one of three findings: a TERT promoter mutation: A change in the switch that controls the TERT gene. It keeps tumor cells from aging out. It is one of several findings your team reads together to name the tumor. See the glossary promoter change, extra copies of EGFR, or an extra chromosome 7 together with a missing chromosome 10. Any one of those is enough. It is a glioblastoma, and it is grade 4.

So a report can say the cells looked lower grade and still land here. Nobody changed their mind and nobody got it wrong. The gene results came in after the first look, and they are what the rules go on now.

Molecular markers explains each of those results.

Where does it grow, and why does it cause these symptoms?

A side view of the brain with each part labeled in plain words.
The parts of the brain, in the words this site uses. Image: Made for BrainHarbor. CC0 1.0 (public domain).

Most glioblastomas grow in the large upper part of the brain. That part handles movement, speech, thinking and vision. So the first symptoms are often on one side of the body, or in speech, or in behavior. Which ones come first depends on where in that area the tumor sits.

Most people are told what they have long before anyone explains what it is doing. These are the ways a tumor in the brain causes symptoms. They overlap, and most people have more than one going on at once. Which of them apply to you depends on what your tumor is and where it sits.

It takes up room. The skull is a closed box. It cannot stretch. So anything new inside it has to push on something. The tumor and any swelling around it together take up space and press on nearby parts of the brain.

It can make the brain around it swell. This one surprises people, and it is worth understanding. Fluid builds up in the brain tissue near the tumor. That swelling plays a major part in deciding what symptoms you get. Some of what you are feeling may not be the tumor itself. It may be the swelling around it. That is why medicines that bring swelling down can change how somebody feels, without the tumor being any different than it was.

Pressure can build up inside the head. When the pressure inside the skull rises, there is a pattern doctors watch for: headaches that are worse in the morning, feeling sick to your stomach and throwing up, odd eye movements, seizures, and being confused or very drowsy. Not everybody with raised pressure has all of it, and some people have almost none of it. If this pattern is new for you, it is worth a phone call rather than a wait. If you have a shunt, it means getting help right away.

It can set off seizures. A tumor and the irritated brain around it can upset the normal electrical activity of that part of the brain. For some people a seizure is the first sign that anything is wrong.

It can block the flow of fluid. The brain makes a fluid that circulates around it and drains away. A tumor sitting in the wrong place can block that flow, so the fluid backs up and the pressure goes up. This is more likely with tumors near the narrow channels the fluid passes through. It can be treated, and the usual treatment is a shunt. That is a thin tube that carries the fluid to another part of the body, where it is absorbed. It is the word your team will use. Shunts and hydrocephalus covers what having one is like, and the signs it has stopped working.

Why your symptoms are the ones you have

The short rule: the symptom tells you where, the scan tells you what. A tumor disturbs whatever job the brain does in that spot, so where it sits decides what you notice.

There is one exception, and it is the fluid. When the flow is blocked, what you notice is the pressure rather than the spot: headaches worse in the morning, throwing up, double vision, and feeling unsteady. Those signs are much the same wherever the blockage sits, so they tell you the pressure is up, not where the tumor is. If that is your pattern, the part above called It can block the flow of fluid is the one about you, and it says what can be done. If the pattern is new, the phone call above applies.

If something on this list matches what you have noticed, it is worth writing down and taking to your next appointment. Your team can tell you whether it fits where your tumor actually is.

This list is about what the place explains. The other half of the question is what the place changes: whether an operation is offered, how much of it can come out, and when the place makes something urgent on its own. Where your tumor is, and what that changes is that half.

The growth story, which explains four things at once

This is worth reading slowly, because it is the one paragraph that makes the rest of the page make sense.

A glioblastoma grows quickly. It grows more quickly than it can build blood vessels to feed itself, so oxygen runs low inside it. The cells in the middle, furthest from a blood supply, starve and die. That dead area is what the word necrosis means on your report.

Low oxygen switches on a chemical alarm inside the tumor cells that are still alive. That alarm makes them release a signal telling the body to build new blood vessels. New vessels do get built. But they are built in a hurry, and they come out abnormal: immature, badly formed and leaky.

Those two facts explain almost everything else:

None of that is a reason to expect less of an operation. What surgery does is take pressure off, give the tissue the diagnosis is made from, and leave the other treatments less to work against.

What symptoms does it cause?

The commonest are:

Seizures happen in up to half of people with this diagnosis, and for many people a seizure is what led to the scan.

When to call for help right now

Some things should not wait for the next appointment.

Call an ambulance for any of these. Call 911, or your local emergency number:

A seizure like the ones you usually have, that stops on its own, is not an ambulance call. What to do during a seizure draws the line.

Call your team the same day for any of these:

If you are having chemotherapy, a fever is its own rule. It means calling your team right away, at any hour, not waiting for the morning. An infection during chemotherapy can get dangerous fast, and it is treatable when it is caught early. The fever rule explains why, and what number your team will give you.

In the weeks after brain surgery, a fever is its own rule too, especially with a stiff neck or a bad headache. What comes after a craniotomy has the rest of that list.

If you have a shunt, the signs it has stopped working are their own rule. For you, everything on the same-day list above is a right-away call instead, and so are a few other signs. Get help right away, at any hour: call your team, or go to the emergency department. Signs a shunt is not working has the full list.

If you are not sure whether to call, call. Nobody on that team minds a phone call that turns out to be nothing.

Same day means today, not the next clinic appointment. Ask your team now for the after-hours number, and put it somewhere you will find it at two in the morning rather than somewhere sensible.

What to do during a seizure has the step-by-step, and getting help now is the short version to keep on a phone.

How do doctors find out it is this?

A scan first, then a piece of the tumor, then gene tests on that piece.

How tissue is taken goes through both ways of getting that sample, and what happens if it does not give an answer.

What do the words on my report mean?

The rules for naming brain tumors changed in 2021. If your paperwork was written before that, some of its words are no longer used.

This matters more than it sounds. People read an old report next to a new one, see two different names, and think somebody made a mistake. Usually nobody did. The tumor did not change. The way doctors write it down changed.

Three changes affect almost every report.

Seeing an older name on your own report does not mean it was wrong. It means it was written under the old rules. If you are holding an old report and a new one and they do not match, that is a good thing to take to your team and ask about.

The results that matter most on this particular report:

Your pathology report walks through the document itself, section by section.

If your older paperwork says something different

Two names land on this page more than anywhere else.

So go by the IDH line, not by the old word. If your report says IDH-mutant and glioblastoma together, it was written under the old rules, and astrocytoma is the page for you. If it says IDH-wildtype, this page is yours whatever the older paperwork called it.

That is not just filing. The names were separated because IDH-mutant tumors behave differently, and the treatment conversation is not the same. It is worth asking your team to confirm which one applies to you.

How is it usually treated?

A tumor board is a meeting where specialists look at one person's case together: surgeons, cancer doctors, the lab, and the people who read scans. It tends to happen when a case is complicated or something is hard to read.

You do not go to the meeting. Afterwards, the doctor who knows you best explains what was said.

What they decide is advice, not an order. The choice is still yours. Because you are not in the room, tell your team what matters to you before it happens, so it is taken into account.

There is a standard plan for a newly diagnosed glioblastoma, and most people are offered a version of it.

Why they cannot take it all out

This is the question people most want answered, and the honest answer is in the growth story above. Tumor cells have already spread past the edge that shows on the scan, into brain that has to stay. Surgery removes what can be seen and safely reached. It is not a failure of the operation or the surgeon, and asking for a bigger operation does not fix it.

What surgery does do is take pressure off, give the diagnosis, and give the other treatments less to work against.

MGMT, and what it changes

If the MGMT test comes back methylated, temozolomide is more likely to help you. If it comes back unmethylated, it is less likely to. It is one of the few results on this page that changes a treatment conversation rather than describing the tumor.

It is a fair thing to ask about directly: what was my MGMT result, and what does your team do differently because of it?

Tumor treating fields, the device you wear

tumor treating fields: A treatment that makes it harder for tumor cells to divide. It uses electric fields that switch back and forth. The fields come from pads on the scalp. A box you carry drives them. The box is often called Optune. See the glossary is the name to ask about, and the device is usually called Optune. It delivers alternating electric fields through pads worn on the scalp, and it is used alongside temozolomide after radiation finishes. It is usually started around four to seven weeks after radiation ends. It is for people whose tumor is in the upper part of the brain, and who are managing reasonably well day to day.

The main side effect is skin irritation where the pads sit. It means wearing it at least eighteen hours a day and shaving your head. Some people find that a reasonable trade and some do not, and that is a legitimate thing to weigh rather than a test of how hard you are trying. Living with the device covers what wearing it asks of you, and of the person helping you.

If you are older, or not well enough for the full course

A shorter course of radiation is the preferred plan for people over about seventy, and for people who are less well. It is not a smaller version handed out to save trouble. It gives much the same results with fewer side effects and a better time of it. That is why it is the standard for that group.

Bevacizumab, and one honest note about it

bevacizumab: A drug that acts on the blood vessels a tumor builds. In brain tumors it is used mainly for two things. One is to control symptoms from swelling. The other is to cut down how much steroid someone needs. See the glossary is a drug used for the swelling around a glioblastoma. It can make scans look better and cut down the need for steroids. But in the trials in newly diagnosed glioblastoma it did not help people live longer. Targeted drugs covers what being on it involves, including the rule about surgery.

It is useful for what it is useful for. The thing worth holding on to is the difference between a treatment that improves a picture and one that changes an outcome. That difference is easy to lose in a conversation.

What is treatment actually like, and what is normal afterwards?

The library pages carry the detail: what a craniotomy is like, what radiation is like, and what chemotherapy is like, including the fever rule, which is the one thing to know before you start.

Two things specific to this diagnosis:

Steroids will probably be part of it, and they change how you feel. They work on the swelling described above rather than on the tumor itself. They also affect sleep, appetite, mood and blood sugar. Coming off them is done slowly and on a plan. If you feel unlike yourself on them, that may well be the drug rather than the tumor. Say so rather than putting up with it. Steroids goes through the whole of it, and anti-seizure medicines does the same for the other drug that gets blamed on the tumor.

The weeks after radiation are their own thing. Tiredness often arrives after treatment finishes rather than during it, and it can be heavier than people expect. It is not a sign that something has gone wrong.

Everyday life: work, driving, seizures and tiredness

Driving rules depend on where you live and on your seizure history. Your team knows the rules where you are. Ask directly rather than guessing, and ask again after any change in your medicine or your seizures.

Work and money. Some people keep working and many change what they do or how much of it. Treatment is close to a full-time commitment for the first couple of months. Ask your team early who at the hospital helps with the practical side. There is usually somebody, and people tend to find them late.

Tiredness and changes in concentration, word-finding and patience are common, and they come from the tumor and its treatment rather than from effort.

Follow-up scans, and what to do while you wait

Scans continue after treatment, and the wait between a scan and its result is the hard part for most people. Waiting for results covers what is happening in that gap.

A worse-looking scan does not always mean the tumor has grown. After radiation with temozolomide, a scan can look worse for a while and then settle without any change of treatment. It has a name, pseudoprogression, it usually shows up within about the first three months after radiation finishes, and it can cause real symptoms, so it is not only a picture problem. Telling it apart from real growth sometimes needs a second scan rather than a decision on the day.

If your team says "let us scan again before we change anything", that is usually this, and it is not them stalling.

Follow-up scans, and what the results mean goes through the rest of it: what each scan is compared with, and what the words on the report mean.

If it comes back, or changes

This is a tumor that is expected to come back, and saying so plainly is fairer than letting it arrive as a surprise. Where and when it comes back varies, and your own scans are what answer that rather than anything a page can say.

That is not the end of the options. There may be further surgery, radiation again to a smaller area, a different chemotherapy such as lomustine: A chemotherapy you take as a capsule. You take it now and then, not every day. It lowers your blood counts weeks after a dose. That is why the doses are spaced out. See the glossary, bevacizumab for the swelling, tumor treating fields, or a clinical trial. What fits depends on what was used before, how long the gap was, and where the tumor is.

Clinical trials are worth asking about early, not only when other things have been tried. Ask your team what trials you would be eligible for and what testing would be needed to find out.

The thing worth doing now: ask your team what would make them want to see you before your next appointment, and write the answer down.

Did I cause this?

Almost everybody asks this, usually in the first week, usually in private. It is worth answering plainly.

For most brain tumors, nobody knows the cause. That is the honest state of it. The exact cause of most brain and spinal cord tumors is not fully understood, and there are very few well established risk factors. Tumors start when genes that control how cells grow and divide are changed, and in most cases those changes happen by chance during a person's life. Not because of something done or not done.

Cell phones. They give off a kind of radiation called radiofrequency. It is not the same as the radiation in an x-ray. The energy is too low to damage DNA, and it is not known to cause cancer. The evidence so far is that using a cell phone does not cause brain tumors.

Stress. There is no scientific evidence that stress causes brain tumors, and no data linking stress to a higher chance of getting one. A hard year before a diagnosis is a hard year. It is not a cause.

Something you ate, or did not eat. No food and no diet is an established cause of a brain tumor. It is not on the list of known risk factors at all.

Something you passed on, or caught. Brain tumors are not contagious. Most are not inherited either. A small number of people do have an inherited condition that raises the risk, and if that applies to you, your team will raise it and offer to talk it through.

If you are turning this over at three in the morning, that is ordinary and it happens to nearly everyone. It is also worth saying out loud to somebody on your team, because they have answered it many times and they would rather you asked.

Will my children get this? This is the other half of the same question and it deserves a direct answer. The gene changes that define a glioblastoma, meaning TERT, EGFR and the chromosome 7 and 10 pattern, are changes in the tumor, not in you. They are not in the rest of your body and they are not passed on.

A small number of families do carry an inherited condition that raises the chance of a brain tumor. It is uncommon. Your team can tell you whether anything in your history points that way, and if it does they will offer genetic counseling rather than leave you to work it out.

What might happen over time

The next part is about outlook. Some people want to read it. Some people would rather not. You can skip it and come back another day. Nothing else on this page depends on it.

Show the part about outlookHide the part about outlook

Doctors sometimes describe outlook using numbers. It is worth knowing what those numbers are before you decide whether you want them.

They come from large groups of people treated years ago. That matters here for a particular reason: the rules for naming this tumor changed in 2021, and they moved a group of tumors out of this diagnosis and into a different one. So an older figure may describe a group that included people who would not be given your diagnosis today.

The word you will run into is median. A median is the middle of a group. If you lined everybody up, the median is the person standing in the middle. Half did better and half did worse. It is not a prediction about any one person, and it is not a number of months anybody was handed.

The shape of the group matters as much as the middle. These figures are not spread evenly. There is a long tail of people who do far better than the middle, and those are real people rather than exceptions to be set aside. A median cannot show you that tail.

What shapes your own situation most is your MGMT result, how much of the tumor came out, how well you are managing day to day, your age, and how the tumor behaves over the first months. Those are things your own team can see, and a page written for everybody cannot.

For the person caring for someone with this

If you are the one driving to the appointments, keeping track of the pills, and lying awake at night worrying about them, this part is for you.

You are allowed to ask questions. In one study, families said they were afraid of annoying the doctor by asking too much. One of them was told by a doctor to stop playing doctor. Ask anyway. Write your questions down before you go, and bring a notepad. Two people in the room hear more than one.

Ask who your first call is. Care comes from a lot of people at once, and it is easy to end up as the only one holding it together. Ask the team: who do I call first? Some teams have one person whose job this is, often a nurse. Get the name and the number.

Get two numbers, and know which one to use. One for work hours, one for nights and weekends. Then ask what counts as "call us today" and what counts as "call an ambulance" for this tumor, and write the answer down where you can see it. If you are not sure which it is, call. Nobody on that team will mind.

If they have seizures, read about them before you need to. What to do when someone has a seizure is the one to know by heart. Living with seizures is about the rest of the time: what is safe, what to change, and driving.

Ask to be shown anything you are sent home to do. In that same study, families were sent home to change dressings and give medicines with no training at all. That is not fair to you. Before you leave the hospital, ask someone to show you. Then do it once while they watch.

Say what you notice. You may see a change before they do. Changes in thinking, mood and behavior can show up to the people close by first. Telling the team is not going behind their back. It is something the team cannot learn any other way.

Look after yourself, and let people help. Eat, sleep, and keep your own appointments. Take a little of the day back for yourself. When someone asks what they can do, give them a real job: a meal, a ride, an hour with the kids. Most people want to help and do not know how to offer.

You can talk to somebody about all of this today. See where to get help.

Two things specific to this diagnosis.

The changes you notice may not be the person. Behavior, memory, patience and word-finding can all be affected by the tumor, by the swelling around it and by steroids. It can look like someone choosing to be difficult. It usually is not.

The first few months are the busiest. Surgery, then six weeks of daily radiation, then monthly cycles. Getting somebody to appointments every weekday is the part people underestimate, and it is the thing worth asking for help with early rather than when you are already worn out.

What to ask your team

Where to get support

This is not medical advice. It explains research in plain words. Your care team knows your case. Talk with them before you make any decision about your treatment.

Last reviewed: September 8, 2026

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