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Primitive neuroectodermal tumours (PNET)

Read about primitive neuroectodermal tumours (PNET), its treatment and possible side effects. 

What it is

PNET (pronounced pee net) stands for a group of tumours know as Primitive Neuro Ectodermal Tumours. Doctors use this term to groups these tumours together because the tumour cells look similar under a microscope.

PNETs develop from cells that are left over from the earliest development of the body in the womb. Normally these cells are harmless. But sometimes they can become cancerous.

Types of PNET

There are different types of PNET. These include:

  • medulloblastoma, which develop at the back of the brain in the cerebellum
  • pineoblastoma, these develop deep in the middle of the brain, near to the pituitary gland
  • central nervous system PNET, which develop in the forebrain

Medulloblastoma is the second most common brain tumour in children. But the most common malignant (high grade) childhood brain tumour.

Medulloblastoma can also be diagnosed in young adults. These tumours can grow quickly and are likely to spread to other parts of the brain and spinal cord. 

Diagram showing the main parts of the brain

Diagnosing a PNET

Your doctor will examine you and you may have blood tests to check your general health. Other tests include:

  • CT or MRI scan 
  • biopsy
  • a lumbar puncture to take a sample of the fluid that surrounds your spinal cord



The main treatment is surgery to remove as much of the tumour as possible. 

Some tumours cause a fluid build up in the brain (hydrocephalus). If this applies to you, your surgeon can relieve this in the same operation to remove your tumour. 

Your surgeon might make a hole to drain fluid into another area of the brain (known as a ventriculostomy operation). Or they may put a tube called a shunt in place. This reduces the swelling and fluid collection in your brain. 

Reducing the fluid build up reduces the pressure in your skull and helps to control the symptoms of your brain tumour. 

Posterior fossa syndrome

About 25 out of 100 (25%) people have particular symptoms after surgery. The symptoms are called posterior fossa syndrome and they can be very mild or severe. Symptoms include difficulty talking, swallowing or walking. This syndrome is thought to be more unusual in children.  

Posterior fossa syndrome might develop from one day to a week after surgery. The symptoms usually improve slowly over a few weeks or months. But they may not go away completely in some people. Research is trying to find out what causes posterior fossa syndrome. 


You might have radiotherapy to the brain and sometimes the whole of the spinal cord. About 1 in 5 people (20%) with meduloblastoma have spread to the spinal cord when they are diagnosed. In other people, there is a risk that it will spread. So you have radiotherapy to reduce this risk or treat spread that is already there. 


You might have chemotherapy after surgery. This aims to stop the tumour coming back. You may be treated with radiotherapy at the same time. 

Treatment for children under 3

The specialist will usually avoid using radiotherapy to the whole brain and spine if your child is younger than 3. Their young age makes them more likely to develop long term side effects.

The specialist might recommend chemotherapy instead. This aims to keep your child's tumour under control until radiotherapy is likely to cause less damage.  

In general your child is likely to have high dose chemotherapy with a number of drugs. They might also have radiotherapy just to the area containing the tumour. This way, radiotherapy to the whole brain and spinal cord can be delayed until your child is older. Or it might be avoided altogether. 

There are 3 main types of medulloblastoma:

  • desmoplastic
  • classic
  • anaplastic

Those that occur in very young children tend to be desmoplastic tumours.

These tumours are very sensitive to treatment and can often be cured with chemotherapy on its own. Your child has chemotherapy using a number of drugs given into their vein. They also have chemotherapy into the fluid around the spinal cord (intrathecal chemotherapy).

Coping with a PNET

Coping with a diagnosis of cancer can be difficult, both practically and emotionally. It can be especially difficult if you have a rare cancer, such as a PNET. Being well informed about your cancer and its treatment can make it easier to make decisions and cope with what happens.

Follow up

You have regular appointments with your doctor or nurse after treatment finishes. Your doctor examines you at each appointment. They ask how you are feeling, whether you have had any symptoms or side effects, and if you are worried about anything. You might also have MRI scans on some visits.

How often you have check ups depends on your individual situation.

Research and clinical trials

There may be fewer clinical trials for rare types of cancer than for more common types.

It is hard to organise and run trials for rare cancers. Getting enough patients is critical to the success of a trial. The results won't be strong enough to prove that one type of treatment is better than another if the trial is too small.

The International Rare Cancers Initiative (IRCI) aims to develop more research into new treatments for rare cancers. They are designing trials that involve several countries so that more people will be available to enter trials.

Last reviewed: 
06 Oct 2015
  • Cancer and its management (7th edition)
    Tobias J and Hochhauser D
    Blackwell, 2015

  • Description of posterior fossa syndrome in children after posterior fossa brain tumor surgery
    E Kirk and others 
    Journal of  Pediatriatric Oncology Nursing 1995 Oct;12(4):181-7

  • Improving outcomes for people with brain and other CNS tumours
    National Institute for Health and Clinical Excellence, June 2006

  • Principles and practice of oncology (10th edition)
    VT De Vita, S Hellman and SA Rosenberg
    Lippincott, Williams and Wilkins, 2015. pp1412-1455  

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