What is a schwannoma brain tumour?
Also called vestibular schwannoma, acoustic neuroma, neurilemoma, neurilemmoma, neurolemmoma, or peripheral fibroblastoma, Schwannoma is a type of low-grade brain tumour that develops from schwann cells.
Schwann cells form what is called the myelin sheath, by wrapping themselves around peripheral nerves (neurons) to provide protection and support. Peripheral nerves are those that form a network called the peripheral nervous system (PNS), which lies outside the brain and spinal cord.
Are Schwannomas low-grade (benign) or high-grade (malignant) brain tumours?
Almost all schwannoma brain tumours are classified as grade 1, which is the slowest growing type of brain tumour. They are often referred to as benign (non-cancerous), but many patients and clinicians prefer to describe them as low-grade or “slow-growing”.
Symptoms can get worse over time as schwannomas brain tumours increase in size, but the growth rate can vary significantly between one patient and another. Researchers are working hard to better understand and ultimately control this process.
What are the symptoms of schwannoma?
Due to the wide-ranging function of peripheral nerves, the symptoms of a schwannoma tumour will depend upon where it has formed and what those nerves are controlling.
Symptoms of schwannoma could therefore include:
- Hearing loss that becomes gradually worse
- Tinnitus (ringing in the ear)
- Facial muscle weakness, numbness or pain
- Persistent headaches
- Weakness in the arms or legs
- Balance issues, especially if walking in the dark or on uneven ground
- Poor limb co-ordination (ataxia) on one side of the body
- A hoarse voice or difficulty swallowing
What causes a schwannoma brain tumour?
Most schwannomas occur spontaneously. The cause of a schwannoma brain tumour is, in the majority of cases, the development of fault in a gene called NF2 (which is a gene on chromosome 22 in our DNA).
The NF2 gene provides instructions for the body to make a protein called “merlin”. This protein is also known as schwannomin because it is produced in schwann cells within the nervous system.
The merlin protein acts as a tumour suppressor. In other words, it prevents cells from growing and dividing in an uncontrolled way. When it fails to carry out this function, tumours form from the schwann cells that surround the nerves. Researchers also suspect that merlin helps to control cell movement, cell shape and communication between cells.
The NF2 fault can lead to the genetic disease called neurofibromatosis 2. Anyone diagnosed with any form of neurofibromatosis would be transferred to a specialist team to ensure that patients are cared for by clinical experts in treating this condition.
Schwannomatosis is another genetic disease that can lead to a schwannoma brain tumour. Schwannomatosis tends to be diagnosed in early adulthood. It can be preceded by chronic pain, sometimes in areas where there are no tumours, due to the fact that pain signals originating from nerves where tumours are causing pressure can sometimes be felt at distant sites within the body.
Are there different types of schwannoma?
Schwannoma brain tumours can be given a different name that describes where it is located.
For example, a schwannoma wrapped around the vestibulocochlear nerve in the inner ear – responsible for balance and hearing – would be called an acoustic neuroma and could also be known as a vestibular schwannoma.
Schwannomas may also be referred to as neurilemoma, neurilemmoma, neurolemmoma, or peripheral fibroblastoma.
What is the best treatment for schwannoma brain tumours?
Some patients will require surgery. In some cases, radio and/or chemotherapy may also be required. Conversely, some schwannomas grow so slowly that patients simply need to be monitored using regular scans, and may not require treatment.
Some schwannomas can be completely removed by surgery, whilst others may be in positions in the brain where there is a risk of causing harm. For example, if a patient has an acoustic neuroma there may be a risk to their hearing and balance if surgery is undertaken.
In these cases, the priority for the neurosurgeon will be to ensure that they remove as much of the tumour as possible whilst avoiding any damage to these critical structures.
If the tumour grows back, surgery may be offered again to reduce tumour size again.
Schwannoma stereotactic radiotherapy: This is a highly targeted form of radiotherapy that may be used to treat small schwannomas (usually less than 3cm diameter), dependent on their position.
Schwannoma radiotherapy: Radiotherapy is rarely used for slow-growing forms of schwannoma in order to avoid damage to the delicate nerves that they are wrapped around. For malignant or high-grade schwannomas, radiotherapy would be used to help prevent recurrence after surgery.
Schwannoma chemotherapy: It is rare to treat slow-growing schwannoma tumours using chemotherapy drugs. For malignant or high-grade schwannomas, the cells will be dividing more rapidly and therefore chemotherapy is likely to be offered.
Molecular profiling of schwannoma: This can clarify the status of various genes, as well as the methylation profile of the tumour. Methylation means adding, removing or replacing a methyl group (CH3) on a molecule (for example, DNA) that then influences the way in which molecules behave (for example, switching genes on the DNA on and off).
There is a lot of research in schwannoma pathology at the moment to clarify which molecular characteristics can be relied upon to guide treatment decisions. It also enables researchers to explore drugs that can target specific genetic mutations, leading in the future towards more effective, personalised treatment protocols.
How will we find a cure for schwannoma?
Research taking place at three of our Centres of Excellence will help lead towards finding a cure for schwannoma.
Our Brain Tumour Research Centre of Excellence in the University of Plymouth is Europe’s leading research institution for low-grade brain tumours, and has a strong focus on schwannoma. They have developed an all-human cell model of schwannoma, developed from tissue samples donated by patients who have undergone surgery. This model is being used in laboratory experiments designed to learn more about the causes and behaviour of schwannoma brain tumours, and ultimately to find a cure by developing targeted drug therapies.
Our research team at our Imperial College Centre of Excellence are collaborating with our Plymouth Centre, comparing the profile of brain tumour cells and normal brain cells. Using state-of-the-art techniques, they identified specific changes in the tumour cells and, significantly, have determined how they might overcome the changes, stopping the tumour in its tracks! This exciting research development has brought a focus on certain drugs already used for kidney and liver cancer but never before for brain tumours. This discovery is now forming the basis for a new clinical trial.
Scientists at our Brain Tumour Research Centre of Excellence in the University of Portsmouth also collaborate with the Plymouth Centre on some aspects of schwannoma research. Their findings can be used to develop treatments that target particular molecular pathways and hence influence the processes that they control.