A medulloblastoma/PNET is a malignant (cancer) tumour formed from primitive or poorly developed brain cells.

In this section

Most of these tumours originate in the lower back part of the brain (called the cerebellum) and are called medulloblastomas.

When they occur in other parts of the brain they are called PNETs (Primitive Neuro Ectodermal Tumours). If a PNET occurs in the area of the brain called the pineal gland, then the PNET is known as a pineoblastoma. All PNETs can sometimes spread (disseminate or metastasise) to the spinal cord through the cerebrospinal fluid. They rarely spread to other organs of the body.

Who gets medulloblastoma / PNET?

Less than 90 children a year develop medulloblastoma or PNET in the UK. However, it is still the most common malignant brain tumour in children, representing 20% of all childhood brain tumours. They are most common in children between the ages of three and eight, and are slightly more common in boys than girls. They can also be found in adults but are extremely rare.

Like most brain tumours the cause of medulloblastoma or PNET is usually unknown.

Signs and symptoms

The symptoms are usually due to increased pressure in the head (raised intracranial pressure). Symptoms include:

  • nausea and vomiting (most common)
  • lethargy and irritability
  • headaches
  • clumsiness
  • difficulty with tasks like handwriting
  • gradual decline in school work
  • changes in personality and behaviour
  • abnormal gait (the way the child walks).

If the tumour spreads to the spinal cord, the signs and symptoms may include:

  • back pain
  • difficulty walking
  • problems with bowel and bladder control.

Tests / investigations

We will need to carry out some tests to find out as much as possible about the type, position and size of the tumour. This is will help us to decide on the best treatment for your child. These tests include:

  • CT scan – it is likely that a CT scan of your child’s brain was carried out at your local hospital. Although MRI scans are usually the best way of seeing the tumour and the effects of treatment, sometimes CT scans are also used.
  • MRI scan – this scan allows us to see the brain and spine in great detail and is used regularly to diagnose and follow the effect treatment is having on your child’s tumour.
  • Lumbar puncture – this is carried out under general anaesthetic about 14 days after surgery, to look for any malignant cells in the cerebrospinal fluid.


Staging is a measure of how far the tumour has spread beyond its original site. The staging system we use for medulloblastoma / PNET is:

  • M0: No evidence of metastases.
  • M1: Tumour cells found in cerebrospinal fluid (lumbar puncture cerebrospinal fluid test).
  • M2: Tumour spread beyond original site but still in the brain.
  • M3: Tumour deposits (seeds) in the spine that are easily seen on MRI scan.
  • M4: Tumour spread to areas outside the central nervous system (brain and spine).

Treatment of medulloblastoma / PNET

The treatment used for medulloblastoma or PNET depends on where the tumour is, if it has spread and the age of your child. Common treatments include:


All children will have an operation to confirm the diagnosis, relieve pressure and try to remove as much of the tumour as possible.


Radiotherapy is often used after surgery to destroy any remaining malignant cells. As medulloblastoma / PNET may spread through the cerebrospinal fluid to the spinal cord, radiotherapy is given to the brain and spinal cord.

However, in young children (especially under the age of three years), we may delay, reduce or possibly avoid radiotherapy. This is because of the significant effects of radiotherapy on a younger child’s brain.

See the Children’s Unit booklet Radiotherapy treatment for more details on this type of treatment.


Chemotherapy is given together with surgery and or radiotherapy to treat the tumour. Treatment with anti-cancer drugs is used to destroy the cancer cells. It is usually given by injections and drips into a vein (intravenous infusion).

The type of chemotherapy will vary according to whether the tumour has spread, if radiotherapy is to be used and the age of the child. Some children may need high-dose chemotherapy with a stem cell transplant.

If your child takes part in a clinical trial, the treatment is explained in more detail in a specific trial information sheet. You will be given an outline of the treatment in the form of a ‘road map’.

Clinical trials

Clinical trials are medical research trials involving patients that are carried out to try and find new and better treatments. In cancer, clinical trials are most commonly used to try and improve different forms of treatment such as surgery, radiotherapy or chemotherapy.

The treatment being tested may be aimed at:

  • improving the number of people cured (for example: trying new types of surgery or chemotherapy)
  • improving survival
  • relieving symptoms of the cancer
  • relieving the side effects of treatment
  • improving the quality of life or sense of well-being for people with cancer.

Clinical trials may also involve research aimed at understanding more about the tumour’s biology. You may be asked to allow us to do research on the tumour sample removed at surgery or on blood or cerebrospinal fluid samples.

Well-run clinical trials have led to a significant improvement in the treatment of children with cancer. If you are asked to consider entering your child into a clinical trial you will be given specific information about the trial before deciding whether to take part.

Effects of treatment

Significant progress has been made in the management of children with medulloblastoma / PNET over the last ten years.

The majority of children with a localised tumour removed by the surgeon and who also have intensive chemotherapy and radiotherapy in a reduced dose to the brain and spine are cured. Children who have PNET, an incomplete removal of tumour at initial surgery, or evidence of the tumour having spread, have a poorer outlook.

The treatment of infants is difficult. This is because of the need to delay, avoid or reduce radiotherapy to the brain and spine, because of the damaging effects of radiation on the young developing brain.

General side effects of chemotherapy

Bone marrow suppression (myelosuppression)

Chemotherapy drugs decrease the production of blood cells by the bone marrow for a variable period of time. This results in low red blood cells (anaemia), low white blood cells (neutropenia) and platelets (thrombocytopenia). Your child may need blood or platelet transfusions and will be at increased risk of infections. The doctors and nurses caring for your child will tell you more about these side effects.

Nausea and vomiting

Some of the chemotherapy drugs used may make your child feel sick or vomit. We will give anti-sickness drugs at the same time to stop nausea and vomiting. These are usually very effective.

Sore mouth (mucositis)

Some of the chemotherapy drugs make the lining of the mouth and throat very sore and ulcerated. We will give your child painkillers for this, and explain how to care for your child’s mouth during treatment.

Hair loss

Temporary hair loss is common.

Specific drugs

For details of the side effects of individual drugs please see Macmillan specific drug information leaflets.

What are the possible long-term effects of treatment?

As medulloblastomas are more common in young children and the treatment is given at an important time of the child's development there may be some long-term effects of treatment. These could include growth and hormonal changes, reduced fertility, behavioural changes, possible learning problems and difficulties with coordination. Hearing and visual disturbances can result from both tumour and treatments. There is a small risk of developing a second cancer later in life.

All children are seen after treatment is finished in our long-term brain tumour follow-up clinic. We will see your child at regular intervals indefinitely so that we can help with any long-term effects of the treatment.