What Is a Glioblastoma?

Medically Reviewed By Teresa Hagan Thomas PHD, BA, RN
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Glioblastoma is the most common type of brain tumor in adults. It is also the most aggressive. Currently, the treatment plan for glioblastoma includes surgery to remove the tumor, radiation, and chemotherapy. While treatment is improving, a cure does not exist at this time and the prognosis is poor. Current research focuses on immunotherapy, which gives hope for higher survival rates in the future.

Read on to learn more about glioblastomas, the symptoms, what primary and secondary tumors mean, and what the risk factors are. Learn how doctors diagnose the tumor and what the treatment entails.

What is glioblastoma?

Man holding his head
Studio Firma/Stocksy United

A tumor is a mass of abnormal cells growing without regulation. Tumors typically occur due to a problem with the genes that regulate cell growth. Tumors can be noncancerous (benign) or cancerous (malignant).

Glioblastomas are the most common brain cancer in adults, making up 35–40% of all malignant brain tumors. In the United States, there are about 14,000 cases diagnosed each year.

Your brain is made up of four lobes: the frontal lobe, two temporal lobes, and the occipital lobe. Glioblastomas typically grow in one of these four lobes. However, sometimes they grow in the brain stem or spinal column as well.

The World Health Organization (WHO) has a grading system for tumors based on how unusual the cells look under a microscope and how quickly the tumor is likely to spread and grow.

The grades of brain tumors are:

  • Grade I (low grade): The cells of this tumor look typical under the microscope and spread slower than tumor cells in the other grades. These types of tumors do not usually spread to other parts of your body, and they can be cured if completely removed by surgery.
  • Grade II: These tumor cells grow slower than grades III and IV but sometimes do spread into other nearby tissues. They may come back even if removed.    
  • Grade III: These tumor cells look different from regular cells. They grow quickly and can spread rapidly to other central nervous system tissues.
  • Grade IV: These tumor cells look extremely unusual and spread and grow faster than other brain tumor cells. Sometimes, there are areas of dead cells (necrosis) inside the tumor. This type of tumor is usually not curable.

Necrosis is a classic sign of most glioblastomas, which are grade IV tumors.  

What are the symptoms of glioblastoma?

Symptoms can come on suddenly, or you may experience a gradual progression. Symptoms depend on the location of the tumor and can include:

Primary vs. secondary brain tumors

According to the National Institute of Health (NIH), tumors can be primary or secondary.

  • Primary tumors: These are tumors that start to grow in your brain or spinal cord. They are either benign or malignant.
  • Secondary tumors: These are tumors that form after cells break away from a primary tumor that is growing somewhere else in your body. For example, this would be the case if you had lung cancer and some of the cells from the tumor broke free and began growing in your brain. Secondary brain tumors are more common than primary tumors.

A glioblastoma is a primary tumor and rarely spreads outside the brain.

What are the risk factors and causes of glioblastoma?

Researchers have studied many environmental and occupational exposures, but have made no specific links to causes for glioblastomas.

At this time, researchers have identified very few risk factors. However, radiation to the central nervous system or head increases your risk of getting a glioblastoma.

Incidence rates are slightly higher in men than in women, and higher in Caucasians than other ethnicities.

How is glioblastoma diagnosed?

If your doctor suspects that you are having neurological problems caused by a tumor, they will typically refer you to a neurologist.

The neurologist will usually perform a neurology exam in the office.

This exam will assess your:

  • senses
  • hearing and speech
  • vision
  • reflexes
  • coordination and balance
  • mental status

This gives an idea of what part of the brain could be causing the neurological problems.

Next, your neurologist may refer you for some diagnostic scans of your brain.

  • Computed Tomography (CT scan): CT scans are not the standard way to evaluate a tumor, but they are a quick way to tell if this is an emergency or not.
  • Magnetic Resonance Imaging (MRI): This is the gold standard for diagnosing a brain or spinal tumor. These scans have a higher resolution and much more detail. An MRI can see blood flow to the tumor and how dense the tumor is.

On an MRI, a glioblastoma will show up as an irregular mass with a dark center of necrotic cells.

How is glioblastoma treated?

As soon as a tumor is found, surgery to remove the tumor is typically scheduled as soon as possible. However, these tumors are sometimes very difficult to remove because of the their locations.

Once the surgery is completed, the next treatment is typically a 6-week course of radiation along with chemotherapy. The goal of these treatments is to attack the tumor cells that could not be removed during surgery.

These treatments typically only slow the growth of cancer but do not cure it.

There is ongoing research on a new immunotherapy treatment to slow or stop the tumor’s cell growth. This brings hope that in the future the outlook will be more positive.

Click here to learn more about brain tumor treatments.

What is the prognosis for glioblastoma?

The prognosis for someone with a glioblastoma diagnosis is poor.

Even after surgery, radiation, and chemotherapy, 70% of people with these tumors see their tumor grow within a year of being diagnosed.

Less than 5% of people survive 5 years after diagnosis.


Glioblastoma tumors are rare but very aggressive and difficult to treat.

Treatment includes surgery, radiation, and chemotherapy. While this may not cure glioblastoma, it can slow its growth.  

Although improvements have been slow, researchers look to the future with optimism. With continued research, hopefully, they will be able to improve treatment options for glioblastoma.

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Medical Reviewer: Teresa Hagan Thomas PHD, BA, RN
Last Review Date: 2022 Apr 21
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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