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What is a glioblastoma?

Glioblastomas are the most common high grade (cancerous) primary brain tumour in adults. They can also occur, rarely, in children. Glioblastomas belong to a group of brain tumours known as gliomas, as they grow from a type of brain cell called a glial cell.

Glioblastoma is the more common name for a type of brain tumour called a grade 4 astrocytoma.

Glioblastoma are 'diffuse', meaning they have threadlike tendrils that extend into other parts of the brain. They are fast growing and likely to spread. You may also hear them called glioblastoma multiforme, GBM or GBM4.

There are different types of glioblastoma:

  • Primary - this means the tumour first appeared as a grade 4 glioblastoma (GBM)
  • Secondary - this means the tumour developed from a lower grade astrocytoma

What causes glioblastoma?

There is nothing you could have done, or avoided doing, that would have caused you to develop a brain tumour.

As with most brain tumours, why glioblastomas begin to grow is not known. The Brain Tumour Charity is funding research into possible causes, focussed around our genes.

You can read more about how brain tumours are formed.

Diagnosing a glioblastoma

If your doctor (GP or A&E doctor) suspects you have a glioblastoma, they may examine the back of your eye and look for changes caused by increased pressure in the skull. If they still suspect a tumour, they will make an urgent oncology referral either directly for a scan or to a specialist, such as a neurologist (a specialist in diagnosis and non-surgical issues of the brain and nerves).

Neurological examination

The specialist will ask questions about your health and give you a physical examination.


You will then have one or more further tests, such as an MRI or CT scan to establish whether a brain tumour is present.

Sometimes you are sent for the scan directly by your GP, so you may have this before you see the specialist for the neurological examination.

For some people, their first symptom may be a seizure, so they are seen as an emergency. In this case they may also be given a scan as their first test, after which their case will be referred to a neurooncology MDT (multi-disciplinary team) followed by a consultation with the neurologist/neurosurgeon.


If, following the scan, a tumour is found, and the tumour is in an area of the brain which can be operated on, a biopsy (small sample of the tumour) may be taken from your tumour to allow for more accurate diagnosis of the tumour type.

Learn more about how brain tumours are diagnosed

Treating glioblastoma

The current gold standard (ideal) treatment for patients diagnosed with glioblastoma, if they’re well enough, is surgery to remove as much of the tumour as possible, followed by chemoradiation (chemotherapy and radiotherapy), as soon as the surgical wound is healed.

Before a biopsy or surgery, you may like to ask about the possibility of biobanking some of the tissue from your tumour.

Biobanking means storing a sample of your tumour. Doing this may enable you to be a candidate for clinical trials in the future and also have any relevant genetic (biomarker) tests.

Different trials may require your sample to be stored in a particular way. Speak to your healthcare team, to make sure your sample is stored in a way that doesn’t prevent you from taking part in certain trials or having certain treatments, e.g. immunotherapy

Learn more about current treatment options and emerging treatments for glioblastoma

Get support

If you need someone to talk to or advice on where to get help, our Support and Information team is available by phone, email or live-chat.

If you have further questions, need to clarify any of the information on this page, or want to find out more about research and clinical trials, please contact our team:

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0808 800 0004 (free from landlines and mobiles)

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