In most cases, we do not know what causes a brain tumour. We do know that they are not infectious. You can't catch a brain tumour. There are a few risk factors that we do know about. Cancerous brain tumours are more common in males than females. Non cancerous brain tumours, and tumours where the diagnosis is unknown, are more common in females.

Previous cancers
People who have had cancer as a child have a higher risk of developing a brain tumour later in life. People who have had leukaemia or non Hodgkin lymphoma as an adult also have an increased risk. There is some evidence that there is an increased risk of brain tumours in adults who have had other types of cancer but more research is needed to confirm this.

The increase in brain tumour risk may be due to the treatment for the previous cancer, such as radiotherapy to the head. Giving the cancer drug methotrexate into the fluid around the spinal cord (intrathecal methotrexate) for the treatment of leukaemia has been shown to increase the risk of brain tumours. It is important to remember that any increase in brain tumour risk from cancer treatment is small compared to the risk of not having the treatment for the original cancer.

Age
People can get brain tumours at any age. Generally speaking, as we get older our risk of brain tumours increases. But there are many different types of brain tumours and some are more common in younger adults. Overall, more brain tumours are diagnosed now than in the 1970s. This increase in rates is thought to be mainly because we are getting better at diagnosing and collecting data on brain tumours.

Around 400 children (under age 15) are diagnosed with brain tumours in Great Britain each year, so they are quite rare. But brain tumours are the 2nd most common type of cancer in children. Around 300 teenagers and young adults (aged 15 to 24) are diagnosed with brain tumours in the UK each year. They are the 4th most common type of cancer in this age group.

Medical radiation
Exposure to radiation is the only definite risk factor we know about. Types of brain tumours called meningiomas and, to a lesser extent, cancerous (malignant) gliomas, are more common in people who have had radiotherapy, CT scans or X-rays to the head. It is important to remember that X-rays and CT scans are very important in diagnosing illness so that you have the right treatment. Doctors keep medical exposure to radiation as low as possible.