Overview
Brain tumours comprise a mixed group of neoplasms originating from intracranial tissues and the meninges. Some are benign but others are aggressively malignant. Each has its own unique characteristics but unlike tumours in most other areas of the body, even benign intracranial tumours can be lethal. A short description of the more common brain tumours is given in the Cancer Types section below.
The brain is also a common site for cancers that have spread from other parts of the body including the lung, breast and digestive system. These secondary cancers (metastases) are mentioned only briefly in the Cancer Types section.
The brain is made up of 100 billion neurones, each of which is connected to 10,000 other neurones. The brain also contains astrocytes, oligodendrocytes and ependymal cells. These are all types of glial cells which provide support, nourishment and protection for neurones.
The incidence of brain tumours increased by approximately 10% between 1991-2000.
Brain tumours are the fastest growing cause of cancer death among those over the age of 65.
Brain tumours are the most common type of solid tumour in children.
The cure rate for most malignant brain tumours is lower than most other cancers.
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Key Figures
| Total number of new cancer cases in Europe (2006) |
3.2 million |
| Total number of cancer deaths in Europe (2006) |
1.7 million |
| Number of new brain and central nervous system tumours in Europe (2006) |
25,000 per annum |
The US National Cancer Institute’s figures for brain tumours are:
The less common primary brain tumours that make up the rest of the figures are pituitary tumours, lymphomas, oligodendrogliomas, ependymomas, low-grade astrocytomas and medulloblastomas in decreasing order of frequency.
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Cancer Types
Brain tumours do not metastasise outside the CNS.
Gliomas
About half of all brain tumours are gliomas. There are four main types of glioma: astrocytoma, ependymoma, oligodendroglioma and a mixed glioma (which as the name suggests is a mixture of the other types).
- Astrocytomas are the most common type of glioma and occur in both adults and children. Astrocytomas develop from cells called astrocytes and vary in the speed that they grow and how definite the boundary is between the tumour and the rest of the brain. Astrocytomas are subdivided into:
- Ependymomas are tumours that can affect children and young adults. They develop from cells called ependymal cells which repair damaged nerve tissue. On rare occasions, ependymomas will spread through the cerebrospinal fluid within the brain and spinal cord.
- Oligodendrogliomas are tumours found in adults that develop from oligodendrocytes, which make myelin (the substance that covers the nerve axons). Oligodendrogliomas vary in how fast they grow and whether or not they will spread to other parts of the nervous system.
- Mixed Gliomas are a mixture of different types of glioma, and so vary in how they grow and whether or not they will spread to other areas. In general, these tumours behave very much like astrocytomas.
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Acoustic Neuroma
Acoustic neuromas grow in the auditory nerve that connects the ear to the brain and controls hearing and balance. They often cause deafness on the affected side. They are slow-growing and do not spread to other parts of the brain or elsewhere in the body. They are most often found in middle aged and older people. However, younger people with neurofibromatosis can also develop these tumours.
Craniopharyngiomas
Craniopharyngiomas are tumours that tend to affect children, teenagers and young adults. They do not usually spread but can affect vision and hormone balance - resulting in weight gain and growth problems in children.
Haemangioblastomas
Haemangioblastomas grow from blood vessels. They tend to be slow-growing and do not spread to other parts of the brain.
Lymphomas
Lymphomas can start in the brain, particularly in people who have had an organ transplant or have AIDS, because their immune systems are suppressed. Lymphomas in the brain and spinal cord are not the same as lymphomas found in the rest of the body and tend to be more difficult to treat.
Meningioma
Meningiomas are the second most frequent form of brain tumour and account for approximately 25% of all brain tumours in adults. They usually affect older people and women. Meningiomas are tumours that grow from the meninges, the tissues that cover the brain. They are not usually cancerous but depending on their location in the brain can cause significant symptoms, usually due to the pressure that they apply on surrounding structures.
Pineal Gland Tumours
Pineal gland tumours are rare. They start in the pineal gland, which makes melatonin.
Pituitary Tumours
Pituitary gland tumours are usually benign and curable. The pituitary gland produces a number of hormones and so controls a wide range of body functions. Tumours can cause too much or too little of these hormones to be produced. They also have other effects when they press on nearby structures, most importantly the optic nerves connecting the eyes to the brain. Pituitary tumours include:
Primitive NeuroEctodermal Tumours (PNET)
Medulloblastoma is the commonest form of primitive neuroectodermal tumour. The tumours tend to grow in the cerebellum (responsible for balance and coordination) and are the most common brain tumour in children. They can also affect young adults. Medulloblastomas can grow very quickly and may spread to other parts of the brain and spinal cord through the cerebrospinal fluid.
Secondary Brain Tumours
Other forms of cancer can spread to the brain through the blood stream - the most common being breast, lung and colon cancers. Often there will be just one, two or three of these tumours present. If they are detected at an early stage using CT or MRI scans, some can be treated using surgery or various forms of radiotherapy.
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Causes of Brain Tumours
The cause of most brain tumours remains unknown.
The only two proven risks are high doses of radiation to the head (for example in people previously treated with radiotherapy) and associated with rare genetic conditions, including neurofibromatosis, in which acoustic neuromas and meningiomas are more likely to develop.
Exposure to electromagnetic fields from power lines and electronic devices such as mobile and cordless phones has not been proven to be a risk factor, although there is a strongly held view in some quarters that use of mobile and cordless phones should be kept to a minimum.
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Prevention of Brain Tumours
There are as yet no known means of preventing brain tumours. Early diagnosis depends on astute clinical diagnosis which is often difficult when presenting symptoms are non-specific.
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Common Symptoms
The effects of interference with brain function will vary according to the part of the brain which is affected. Specific symptoms, which can also indicate which part of the brain is affected, include:
- numbness
- sensory changes or weakness in a particular part of the body
- loss of coordination (which can also be confined to one part of the body)
- personality changes
- speech problems.
Headaches can be due to a number of causes. Although it is rare that this is the reason for a headache, they can be the result of increased pressure on the brain as the tumour grows within the confines of the skull. Typically, this headache is worse in the morning and may be associated with vomiting.
Brain tumours can also cause convulsions, visual problems, depression, confusion and personality changes.
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Diagnostic Tests
There are a number of tests that can be used to diagnose brain tumours.
Various types of brain scan, including a CT (Computerised Tomography) or MRI (Magnetic Resonance Imaging) scan, will often confirm the presence of a brain tumour. However, it is only through a biopsy - taking a sample of tissue from the tumour, or sometimes taking cerebrospinal fluid and examining it for cells – that the various forms of tumour can be identified and an accurate diagnosis made.
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Treatment
Brain tumours can be treated using surgery and radiotherapy depending on the type of tumour that has been found. Chemotherapy tends to be used less often in the treatment of brain tumours, except in children. Childhood tumours are more likely to spread systemically than those in adults.
Surgery
Brain surgery is usually the preferred treatment option for many brain tumours if the tumour is accessible. If removing the tumour is not possible without damaging normal brain tissue, radiotherapy may be the better option. However, surgery may still be required in these cases to obtain a biopsy for diagnosis or to relieve symptoms caused by raised intracranial pressure.
Brain surgery usually involves a craniotomy (cutting a hole in the skull). However, operations on the pituitary gland, for example, will involve operating through the nose and the base of the skull.
The object of surgery is always the same - to remove as much of the tumour as possible without damaging normal brain tissue. Tumour tissue left behind is usually treated with radiotherapy, however, in young children (under 3 years old) chemotherapy may be preferred to avoid long term side effects.
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External Beam Radiotherapy
External beam radiotherapy uses high energy X-ray beams, generated from machines, to kill cancer cells. A course of treatment usually lasts for six weeks. Radiotherapy is usually given using a linear accelerator. It is increasingly used in conjunction with chemotherapy to treat brain tumours – a process known as chemoradiation.
There are a number of new very sophisticated forms of radiotherapy used in the treatment of brain tumours. These are:
- Stereotactic RadioTherapy (SRT) - a form of high-precision radiotherapy that is now becoming available in many centres. SRT provides radiotherapy focused on the whole tumour with very little effect on surrounding normal tissues. This allows the use of very high doses of radiation in 3-8 treatment sessions or fractions over a 2 week period. During SRT, patients are positioned very precisely during treatment to minimise radiation of nearby normal tissues. SRT also includes measures to allow for movement of the tumour during imaging and treatment planning as well as during radiotherapy.
- Radiosurgery - a form of stereotactic radiotherapy where the treatment is given in one long session instead of a number of shorter sessions. Multiple beams of radiation focus precisely on the tumour. In this way, very high doses of radiation can be delivered to a small target area where the cancer is, thereby destroying it.
- Tomotherapy - delivers radiation to tumours with little effect on surrounding normal tissues. The radiation source rotates around the patient and is delivered with extreme precision using thousands of small beams. Using this system, the area around the spinal cord (but not the spinal cord itself) can be treated. Daily CT scans are used to plan the treatment precisely allowing for the smallest of changes in tumour size.
Chemotherapy
Chemotherapy is the use of drugs to kill cancer cells. Treating brain tumours with drugs can be difficult as many drugs do not cross from the blood vessels into the brain. This is called the blood-brain barrier, which is usually very helpful in keeping harmful substances out of the brain. If drugs that do not cross the blood-brain barrier are required in the treatment of a tumour, they can be given directly into the cerebrospinal fluid.
Chemotherapy may be given to try to prevent a brain tumour from recurring after surgery, or to treat recurrences if they occur, to treat a brain tumour where surgery is not possible or to shrink a tumour so that surgery is easier.
But not all brain tumours respond to chemotherapy - for more details see the treatment for specific brain tumours below.
Chemotherapy is often given instead of radiotherapy in young children. This is to avoid the long term side effects of radiotherapy in children under 3 years of age.
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Treatments for Specific Tumours
Slow growing astrocytomas with a clear boundary can often be treated successfully by surgical removal of the tumour. Even if the entire tumour cannot be removed, it may remain inactive or be successfully treated with radiotherapy.
Anaplastic Astrocytoma
Chemoradiation is the standard treatment.
Glioblastoma Multiforme
Chemoradiation is the standard treatment.
Ependymomas
Surgery is used to remove the primary tumour and radiotherapy is used to treat any residual tumour or tumours that cannot be removed surgically.
Chemotherapy is used as an alternative to radiotherapy in very young children (under 3 years old).
Oligodendrogliomas
Surgery with radiotherapy immediately after diagnosis.
Mixed Gliomas
Surgery with radiotherapy immediately after diagnosis.
Acoustic Neuromas
Surgery (which often results in damage to the auditory nerve and deafness on the affected side) or radiosurgery, which is a form of radiotherapy not surgery. This treats small target areas (less than 3 to 4 cm in size) very accurately, causing little or no damage to surrounding structures.
Craniopharyngiomas
Craniopharyngiomas are very difficult tumours to treat because they develop deep in the brain and it is impossible to remove them completely. Surgery combined with radiotherapy is one option for treatment. Another option is stereotactic radiotherapy.
Haemangioblastomas
Surgery, provided that the tumour is accessible, when combined with external beam radiotherapy or stereotactic radiotherapy is often very successful.
Lymphomas
Chemotherapy and corticosteroids. Radiotherapy is used in the treatment of lymphomas which do not respond to chemotherapy.
Meningiomas
Surgery is the treatment of choice but if the tumour is inaccessible, external beam radiation may be used.
Pineal Gland Tumours
Surgery is difficult because the gland lies deep in the brain. If the tumour cannot be completely removed by surgery, radiotherapy and chemotherapy are used.
Pituitary tumours
Treatment depends on the type of pituitary tumour and whether it has spread into the surrounding brain. Surgery, radiotherapy and, in some cases, drugs are all used in treatment.
Medulloblastoma
Surgery, with postoperative radiotherapy to the entire brain and spine as medulloblastomas spread through the cerebrospinal fluid to other parts of the brain and spinal cord, is the preferred treatment option. Chemotherapy has an increasing role in the treatment of these tumours.
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Prognosis
Many factors affect prognosis. These include the type of brain tumour, its site in the brain, how advanced it is, its rate of growth and infiltration of neighbouring parts of the brain, its propensity to spread to other areas of the brain and central nervous system, as well as the patient’s age, general health and their individual response to treatment (which will vary).
Because there are so many different types of brain tumour (most of which vary in the rate of growth and response to treatment) we have chosen not to quote figures as these are likely to be unhelpful.
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Key Trends
High-grade (anaplastic) gliomas are becoming more common in general and are more common with increasing age.
Chemoradiation is being used more and is becoming the standard treatment in many forms of brain tumour.
Secondary brain tumours (metastases) from cancers of the lung, breast, gastrointestinal tract and other sites are now treated in many centres.
Sophisticated forms of radiotherapy (including stereotactic radiotherapy, radiosurgery and tomotherapy) are now being used to treat a wide range of brain tumours.
New forms of imaging (functional imaging) allow more precise diagnosis and treatment planning.
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Important Research Areas
- The use of gene profiling to determine which patients are best suited to particular treatments, so avoiding toxic side effects of treatment in patients where the treatment is unlikely to succeed.
- New ‘molecular targeted agents’ and their use in the treatment of various forms of brain tumour. These include monoclonal antibodies and small molecules which target cell growth pathways and may be investigated for their ability to enhance the effectiveness of radiotherapy as well.
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