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Brain tumour
A guide for patients and carers
What is a tumour?
What is a brain tumour?
The brain is made from two sorts of cells: neurones or nerve cells and supporting or ‘glial’ cells. Neurones allow the brain to send messages to other parts of the body.They also operate higher mental functions such as memory, personality and ideas. The supporting cells (glial tissue) provide scaffolding for the neurones. The brain is covered by a series of membranes or linings (the meninges).
Tumours of the brain may arise if any of these types of cell grow abnormally, in which case they are called primary tumours. If cells have spread to the brain from a cancerous tumour in another part of the body, they are known as secondaries or metastases.
What causes brain tumours?
Why tumours occur is not yet known with any certainty. Why some tumours are benign (non-cancerous) and others are malignant (cancerous) is also unclear. It used to be thought that some tumours were brought on by head injuries, but we now know that this is not the case. Unlike lung cancer, where a strong link to smoking has been established, we have not been able to find clear risk factors for the development of brain tumours.
The majority of tumours are not inherited and cannot be passed on to children. If a relative has also had a brain tumour, this can almost certainly be put down to coincidence.
A minority of tumours are familial, which means they can be traced to an abnormal gene which may be passed on to other family members - but this is exceptionally rare. It is very unlikely that your tumour is hereditary, but do check this out with the medical team caring for you if you are concerned about this.
Some benign tumours grow for many years and reach a large size before being detected. Malignant tumours tend to grow more rapidly and will have been present for a shorter period when they are discovered. The onset of symptoms does not therefore tell us how long the tumour has been present or indicate whether it is cancerous or non-cancerous.
Distant spread or metastases
The most common sorts of brain tumour are those which have spread from malignant primary tumours elsewhere in the body. These secondaries or metastases are always malignant. Malignant primary tumours of the breast, lung, prostate and sometimes bowel are the usual sources of brain metastases.
Primary tumours: benign or maligant?
A malignant tumour invades surrounding tissues, and as described above may also spread to distant sites (metastasize). The degree to which the tumour invades surrounding tissue tells us how malignant it is – a tumour may be termed low grade, meaning it does this slowly (over many years) or high grade (sometimes a few months). Brain tumours are commonly graded between one (low grade) and four (high grade), which means it may lie anywhere between these extremes. However, this does not necessarily relate to sensitivity to treatment.
Primary malignant brain tumours very rarely spread from the brain, but they do cause trouble by invading the fluid that bathes the brain (the cerebrospinal fluid).
A benign tumour does not invade surrounding tissues or send secondaries to other parts of the body, but it can grow to a considerable size and damage surrounding tissues by pressure. Benign brain tumours are always primary - i.e. they start in the brain.
Other terms used to describe brain tumours
Many words are used to describe tumours.These include swelling (the word tumour literally means "a swelling"), growth (because they are formed when cells grow abnormally quickly) and lesion. Lesion is a word used when the medical team are not sure whether the abnormal area seen on the brain scan is a tumour or some other problem, such as an abscess or perhaps an inflammation or haemorrhage in the brain. This is usually the case after a scan has been done, but before the results of a biopsy are known.
The terms ‘cyst’ and ‘abnormality’ are often used by surgeons when they do not yet know what sort of tumour is involved. Finally, the term cancer is sometimes applied to malignant brain tumours, but this term is usually reserved for malignant tumours elsewhere in the body.
If you are confused by the terms used by your doctors, then ask them to explain. They are not deliberately trying to baffle you, it is merely that they often forget how confusing these terms can be.
How common are brain tumours?
Approximately 5,000 people each year in the United Kingdom are diagnosed as having a primary brain tumour. These tumours can occur at any age. They are more common in elderly people, but are also the most common cancer after leukaemia to affect children. Approximately 1,500 of these tumours are benign.The remainder are malignant.
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